MATRICES AND DETERMINANTS - Mr. Odoom's Math...

� � � � � � � �MATRICES ANDDETERMINANTSMATRICES ANDDETERMINANTS

c How can you organize data aboutmusic sales?

196

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APPLICATION: Music Sales

When you shop for music, your

purchases matter. Music sales by

people age 15 to 19 years

accounted for about 16% of the

$13.7 billion total music purchases

in 1998. The tables below give the

dollar value of the music sold by

age category in 1997 and 1998.

Think & Discuss

1. From 1997 to 1998, how much did sales in the15–19 age category increase? How much did salesin the 20–24 age category decrease?

2. Make a new table that gives the change in the salesin each age category from 1997 to 1998. (Usenegative numbers to indicate decreases.)

Learn More About It

You will find the total Hispanic music sales for 1996and 1997 in Exercise 40 on p. 204.

APPLICATION LINK Visit www.mcdougallittell.com

for more information about music sales.

INT

ERNET

C H A P T E R

4

197

c

1997 Music Sales

Age Sales(years) (billions)

10–14 108.58

15–19 204.96

20–24 168.36

25–29 142.74

30–34 134.2

35–39 141.52

40–44 107.36

45+ 201.3

1998 Music Sales

Age Sales(years) (billions)

10–14 124.67

15–19 216.46

20–24 167.14

25–29 156.18

30–34 156.18

35–39 172.52

40–44 113.71

45+ 247.97

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198 Chapter 4

What’s the chapter about?

Chapter 4 is about matrices and determinants. You can use matrices to organizenumerical data. In Chapter 4 you’ll learn

• how to add, subtract, and multiply matrices, and how to evaluate determinants.

• how to solve linear systems using Cramer’s rule and inverse matrices.

CHAPTER

4Study Guide

PREVIEW

Are you ready for the chapter?

SKILL REVIEW Do these exercises to review key skills that you’ll apply in thischapter. See the given reference page if there is something you don’t understand.

Perform the operation(s). (Skills Review, p. 905)

1. 4 + (º5) 2. º10 º 3 3. (º1)6 º 4(2) 4. 12(5) + 2(º10)

Identify the property shown. (Review Example 4, p. 5)

5. 3(º9) = º9(3) 6. 7 + y = y + 7 7. 4(x º 2) = 4x º 4(2)

Solve the system of linear equations using any algebraic method. (Review p. 149)

8. 2x = 30 9. x º y = 7 10. x º 2y = 24 11. 3x + y = º8x + 4y = 27 3x º 7y = 61 x + 3y = 20 8x º 3y = º10

PREPARE

Here’s a study strategy!

STUDY

STRATEGY

c Review

• multiplicative inverse, p. 5

• coefficient, p. 13

• constant, p. 13

• solution of a system of linearequations, p. 139

c New

• matrix, p. 199

• equal matrices, p. 199

• scalar, p. 200

• scalar multiplication, p. 200

• determinant, p. 214

• Cramer’s rule, p. 216

• identity matrix, p. 223

• inverse matrix, p. 223

KEY VOCABULARY

STUDENT HELP

Study Tip“Student Help” boxesthroughout the chaptergive you study tips andtell you where to look for extra help in this book and on the Internet.

Writing Out the StepsIn this chapter you will perform calculations withnumbers in matrices. When you work with matrices,point your fingers at the numbers you will add,subtract, or multiply. Before calculating, write thenumbers and the operation symbols in the correctlocation of the solution matrix. By doing this step, you are less likely to make a mistake. If you domake a mistake, you can easily trace backwards tofind it.

� � � � � � � �4.1

E X P L O R I N G D ATA

A N D S TAT I S T I C S

4.1 Matrix Operations 199

Matrix Operations

USING MATRIX OPERATIONS

A is a rectangular arrangement of numbers in rows and columns. Forinstance, matrix A below has two rows and three columns. The of this matrix are 2 ª 3 (read “2 by 3”). The numbers in a matrix are its In matrix A, the entry in the second row and third column is 5.

A = F G

Some matrices (the plural of matrix) have special names because of their dimensionsor entries.

NAME DESCRIPTION EXAMPLE

Row matrix A matrix with only 1 row f g

Column matrix A matrix with only 1 column F GSquare matrix A matrix with the same number F Gof rows and columns

Zero matrix A matrix whose entries are all zeros F GTwo matrices are if their dimensions are the same and the entries incorresponding positions are equal.

Comparing Matrices

a. The following matrices are equal because corresponding entries are equal.

F G = F Gb. The following matrices are not equal because corresponding entries in the second

row are not equal.

F G ≠ F G. . . . . . . . . .

To add or subtract matrices, you simply add or subtract corresponding entries. You can add or subtract matrices only if they have the same dimensions.

60

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E X A M P L E 1

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entries.dimensions

matrix

GOAL 1

Add and subtract

matrices, multiply a matrix by

a scalar, and solve matrix

equations.

Use matrices in

real-life situations, such as

organizing data about health

care plans in Example 5.

. To organize real-life

data, such as the data for

Hispanic CD, cassette,

and music video sales

in Exs. 39–41.

Why you should learn it

GOAL 2

GOAL 1

What you should learn

REA

L LIFE

REA

L LIFE

2 rows

3 columns

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200 Chapter 4 Matrices and Determinants

Adding and Subtracting Matrices

Perform the indicated operation, if possible.

a. F G + F G b. F G º F G c. F G + F GSOLUTION

a. Since the matrices have the same dimensions, you can add them.

F G + F G = F G = F Gb. Since the matrices have the same dimensions, you can subtract them.

F G º F G = F G = F Gc. Since the dimensions of F G are 2 ª 2 and the dimensions of F G are 2 ª 1,

you cannot add the matrices.

. . . . . . . . . .

In matrix algebra, a real number is often called a To multiply a matrix by a scalar, you multiply each entry in the matrix by the scalar. This process is called

Multiplying a Matrix by a Scalar

Perform the indicated operation(s), if possible.

a. 3F G b. º2F G + F GSOLUTION

a. 3F G = F G = F G

b. º2F G + F G = F G + F G= F G + F G= F G9

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E X A M P L E 3

scalar multiplication.

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E X A M P L E 2

STUDENT HELP

Study TipThe order of operationsfor matrix expressions issimilar to that for realnumbers. In particular,you perform scalarmultiplication beforematrix addition andsubtraction, as shown inpart (b) of Example 3.

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You can use what you know about matrix operations and matrix equality to solve amatrix equation.

Solving a Matrix Equation

Solve the matrix equation for x and y: 2SF G + F GD= F GSOLUTION

Simplify the left side of the equation.

2SF G + F GD = F G2F G = F GF G = F G

Equate corresponding entries and solve the two resulting equations.

6x + 8 = 26 10 º 2y = 8

x = 3 y = 1

. . . . . . . . . .

In Example 4, you could have distributed the scalar 2 to each matrix inside theparentheses before adding the matrices.

2SF G + F GD = 2F G + 2F G= F G + F G= F G

This illustrates one of several properties of matrix operations stated below.

010 º 2y

6x + 812

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E X A M P L E 4

Let A, B, and C be matrices with the same dimensions and let c be a scalar.

When adding matrices, you can regroup them and change their order without

affecting the result.

ASSOCIATIVE PROPERTY OF ADDITION (A + B) + C = A + (B + C)

COMMUTATIVE PROPERTY OF ADDITION A + B = B + A

Multiplication of a sum or difference of matrices by a scalar obeys the

distributive property.

DISTRIBUTIVE PROPERTY OF ADDITION c(A + B) = cA + cB

DISTRIBUTIVE PROPERTY OF SUBTRACTION c(A º B) = cA º cB

PROPERTIES OF MATRIX OPERATIONS

Look Back For help with propertiesof real numbers, see p. 5.

STUDENT HELP

CONCEPT

SUMMARY

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USING MATRICES IN REAL LIFE

Using Matrices to Organize Data

Use matrices to organize the following information about health care plans.

This Year For individuals, Comprehensive, HMO Standard, and HMO Plus cost$694.32, $451.80, and $489.48, respectively. For families, the Comprehensive, HMOStandard, and HMO Plus plans cost $1725.36, $1187.76, and $1248.12.

Next Year For individuals, Comprehensive, HMO Standard, and HMO Plus will cost$683.91, $463.10, and $499.27, respectively. For families, the Comprehensive, HMOStandard, and HMO Plus plans will cost $1699.48, $1217.45, and $1273.08.

SOLUTION

One way to organize the data is to use 3 ª 2 matrices, as shown.

THIS YEAR (A) NEXT YEAR (B)

Individual Family Individual Family

Comprehensive F G F GHMO Standard

HMO Plus

You can also organize the data using 2 ª 3 matrices where the row labels are levelsof coverage (individual and family) and the column labels are the types of plans(Comprehensive, HMO Standard, and HMO Plus).

Using Matrix Operations

HEALTH CARE A company offers the health care plans in Example 5 to its

employees. The employees receive monthly paychecks from which health care

payments are deducted. Use the matrices in Example 5 to write a matrix that shows

the monthly changes in health care payments from this year to next year.

SOLUTION

Begin by subtracting matrix A from matrix B to determine the yearly changes in

health care payments. Then multiply the result by }

112} and round answers to the

nearest cent to find the monthly changes.

}

112}(B º A) = }

112}SF G º F GD

= }

112}F G

≈ F Gc The monthly deductions for the Comprehensive plan will decrease, but the

monthly deductions for the other two plans will increase.

º$2.16$2.47$2.08

º$.87$.94$.82

º25.8829.6924.96

º10.4111.309.79

1725.361187.761248.12

694.32451.80489.48

1699.481217.451273.08

683.91463.10499.27

E X A M P L E 6

$1699.48$1217.45$1273.08

$683.91$463.10$499.27

$1725.36$1187.76$1248.12

$694.32$451.80$489.48

E X A M P L E 5

GOAL 2

RE

AL LIFE

RE

AL LIFE

Health Care

HEALTH SERVICES

MANAGER

Health services managers inhealth maintenanceorganizations (HMOs) plan

and organize the delivery of

health care.

CAREER LINK

www.mcdougallittell.com

INT

ERNET

RE

AL LIFE

RE

AL LIFE

FOCUS ON

CAREERS

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1. What is a matrix? Describe and give an example of a row matrix, a columnmatrix, and a square matrix.

2. Are the two matrices equal? Explain. 3 4 · F G3. To add or subtract two matrices, what must be true?

4. Use the matrices at the right to find º2(A + B). Is your answer the same as that for part (b) of Example 3? Explain.

5. Rework Example 5 by organizing the data using 2 ª 3 matrices.

Perform the indicated operation(s), if possible.

6. F G º F G 7. F G + F G8. º4F G 9. 6F G º 5F G

10. HEALTH CARE In Example 5, suppose the annual health care costs given inmatrix B increase by 4% the following year. Write a matrix that shows the newmonthly payment.

COMPARING MATRICES Tell whether the matrices are equal or not equal.

11. f g, F G 12. F G, F G

13. F G, F G 14. F G, 3 4ADDING AND SUBTRACTING MATRICES Perform the indicated operation,

if possible. If not possible, state the reason.

15. F G + F G 16. F G + F G17. F G º F G 18. F G + F G19. F G + F G 20. F G + F G21. F G º F G 22. F G º F G}

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PRACTICE AND APPLICATIONS

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GUIDED PRACTICE

Vocabulary Check ✓

Concept Check ✓

Skill Check ✓

A = F G B = F G5º8

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Extra Practiceto help you masterskills is on p. 944.

STUDENT HELP

STUDENT HELP

HOMEWORK HELP

Example 1: Exs. 11–14Example 2: Exs. 15–22Example 3: Exs. 23–32Example 4: Exs. 33–36Examples 5, 6: Exs. 37–47

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MULTIPLYING BY A SCALAR Perform the indicated operation.

23. º4F G 24. 5F G 25. 4F G26. º93 4 27. }

12

}F G 28. 2.53 4COMBINING MATRIX OPERATIONS Perform the indicated operations.

29. F G + 4F G 30. 2F G º F G31. 2F G + 4F G 32. 3F G º 2F GSOLVING MATRIX EQUATIONS Solve the matrix equation for x and y.

33. F G = F G 34. F G + F G = F G35. 2xF G = F G 36. F G + F G = F G

BASEBALL STATISTICS In Exercises 37 and 38, use the following

information about three Major League Baseball teams’ wins and losses in 1998

before and after the All-Star Game. c Source: CNN/SI

Before The Atlanta Braves had 59 wins and 29 losses, the Seattle Mariners had 37 wins and 51 losses, and the Chicago Cubs had 48 wins and 39 losses.

After The Atlanta Braves had 47 wins and 27 losses, the Seattle Mariners had 39 wins and 34 losses, and the Chicago Cubs had 42 wins and 34 losses.

37. Use matrices to organize the information.

38. Using your matrices from Exercise 37, write a matrix that shows the totalnumbers of wins and losses for the three teams in 1998.

HISPANIC MUSIC In Exercises 39–41, use the following information.

The figures below give the number (in millions) of Hispanic CD, cassette, and music video units shipped to all market channels and the dollar value (in millions) ofthose shipments (at suggested list prices). c Source: Recording Industry Association of America

1996 Number of units—CDs: 20,779; cassettes: 15,299; and music videos: 45. Dollar value—CDs: 268,441; cassettes: 122,329; and music videos: 916.

1997 Number of units—CDs: 26,277; cassettes: 17,799; and music videos: 70. Dollar value—CDs: 344,697; cassettes: 144,645; and music videos: 1,260.

39. Use matrices to organize the information.

40. Write a matrix that gives the total numbers of units shipped and total values forboth years.

41. Write a matrix that gives the change in units shipped and dollar value from 1996 to 1997.

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HOMEWORK HELP

Visit our Web sitewww.mcdougallittell.comfor help with Exs. 33–36.

INT

ERNET

STUDENT HELP

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COLLEGE COSTS

Since 1980, collegecosts have risen substan-tially. After adjusting forinflation, costs rose by 48%at public 4-year colleges and 71% at private 4-yearcolleges between 1980 and1995.

RE

AL LIFE

RE

AL LIFE

FOCUS ON

APPLICATIONSA

nnua

l cos

t ($1

000‘

s)

Cost of a 4-Year College

1965 1980 1995

Public Private

0

5

10

15

20


42. COLLEGE COSTS The matrices below show the average yearly cost (indollars) of tuition and room and board at colleges in the United States from 1995through 1997. Use matrix addition to write a matrix showing the totals of thesecosts. c Source: U.S. Department of Education

TUITION ROOM AND BOARD

1995 1996 1997 1995 1996 1997

3 4 3 4PSAT SCORES In Exercises 43 and 44, use the following information.

Eligibility for a National Merit Scholarship is based on a student’s PSAT score.Through 1996, this total score was found by doubling a student’s verbal score andadding this value to the student’s mathematics score. Let V represent the averageverbal scores and let M represent the average mathematics scores earned bysophomores and juniors at Central High for tests taken in 1993 through 1996.

VERBAL SCORES (V ) MATHEMATICS SCORES (M)

Sophomores Juniors Sophomores Juniors

3 4 3 443. Write an expression in terms of V and M that you could use to determine the

average total PSAT scores for sophomores and juniors at Central High from 1993 through 1996. Then evaluate the expression.

44. Use the matrix from Exercise 43 to determine the average total PSAT score forjuniors at Central High in 1996.

U.S. POPULATION In Exercises 45–47, use the following information.

The matrices show the number of people (in thousands) who lived in each region ofthe United States in 1991 and the number of people (in thousands) projected to live ineach region in 2010. The regional populations are separated into three age categories.

1991 2010

0–17 18–65 Over 65 0–17 18–65 Over 65

3 4 3 445. The total population in 1991 was 252,177,000 and the projected total population

in 2010 is 297,716,000. Rewrite the matrices to give the information as percentsof the total population. (Hint: Multiply each matrix by the reciprocal of the totalpopulation (in thousands), and then multiply by 100.)

46. Write a matrix that gives the projected change in the percent of the population ineach region and age group from 1991 to 2010.

47. Based on the result of Exercise 46, which region(s) and age group(s) areprojected to show relative growth from 1991 to 2010?

7,3778,980

14,8322,7075,511

33,82241,09567,33712,42031,125

12,49315,84025,4285,094

13,655

7,0437,857

10,9421,5804,331

31,79136,55453,4718,461

25,001

12,14215,81422,5043,993

10,693

Northeast

Midwest

South

Mountain

Pacific

50.450.050.850.9

49.048.349.449.8

49.048.948.848.6

48.948.948.748.2

1993

1994

1995

1996

3,1284,3454,6995,555

2,9784,1664,4695,368

2,9443,9904,2565,121

1,2832,9867,190

12,920

1,2392,8487,094

12,243

1,1922,6816,914

11,481

Public 2-year college

Public 4-year college

Private 2-year college

Private 4-year college

DATA UPDATE of U.S. Bureau of the Census data at www.mcdougallittell.com INT

ERNET

! " # $ % & '


48. MULTI-STEP PROBLEM The matrices show the number of hardcover volumessold and the average price per volume (in dollars) for different subject areas.

c Source: The Bowker Annual

1995 (A) 1996 (B )

Volumes Average price Volumes Average pricesold per volume sold per volume

3 4 3 4a. Calculate B º A. How many more (or fewer) law volumes were sold in 1996

than in 1995? How much more (or less) did the average music book cost in1996 than in 1995?

b. Calculate B + A. Does the “volumes sold” column in B + A give youmeaningful information? Does the “average price per volume” column in B + A give you meaningful information? Explain.

c. Writing What conclusions can you make about the number of volumes soldand the average price per volume of these books from 1995 to 1996?

49. A triangle has vertices (2, 2), (8, 2), and (5, 6). Assigna letter to each vertex and organize the triangle’s vertices in a matrix. When youmultiply the matrix by 4, what does the “new” triangle look like? How are thetwo triangles related? Use a graph to help you.

TRANSFORMING FIGURES Draw the figure

produced by each transformation of the figure

shown. (Skills Review, p. 921)

50. a 270° counterclockwise rotation about the origin

51. a translation by 2 units right and 4 units down

52. a reflection over the y-axis

MULTIPLYING REAL NUMBERS Find the product. (Skills Review, p. 905)

53. º4(º5) 54. 8(º2) 55. º7(º1)

56. }

12

}(º7) 57. }

56

} • }

37

} 58. 3.2(2.4 + 8.1)

CHECKING SOLUTIONS Check whether the ordered pairs are solutions of the

inequality. (Review 2.6)

59. x + 2y ≤ º3; (0, 3), (º5, 1) 60. 5x º y > 2; (º5, 0), (5, 23)

61. º8x º 3y < 5; (º1, 1), (3, º9) 62. 21x º 10y > 4; (2, 3), (º1, 0)

FINDING A SOLUTION Give an ordered pair that is a solution of the system.

(Lesson 3.3)

63. x + y < 10 64. x º y ≥ 3 65. 3x > yy > 1 y < 12 x ≤ 15

MIXED REVIEW

GEOMETRY CONNECTION

53.4088.5139.2133.92

1,070,000827,000253,000179,000

41.2373.0943.2738.30

1,116,000716,000251,000199,000

Art

Law

Music

Travel

★★Challenge

TestPreparation

()

*( (4, 5) (6, 5)

(2, 2) (8, 2)

+ , - . / 0 1 2

4.1 Technology Activity 207

Using Matrix OperationsYou can use a graphing calculator to perform matrix operations.

c EXAMPLE

The matrices show music sales (in thousands) for a chain of stores during a two-month period. The music formats are CDs and cassette tapes. The categories of music are Rock (R), Country (C), Jazz (J), and Easy Listening (E).

a. Find the total sales for each format and category for May and June.

b. Estimate the sales for July if they are expected to decrease 3% from the June sales.

c SOLUTION

a. To find the total sales in each format and category for May and June, let matrix Arepresent May sales and let matrix B represent June sales. Use a graphingcalculator to enter each matrix. Then find the sum of matrix A and matrix B.

For each matrix, enter the Then enter the data row by To find the sum, select each

dimensions of the matrix. row until all 8 entries have matrix from the matrix menu

been filled for each matrix. and add.

b. To estimate the sales for July, multiply matrix Bby the scalar 0.97. The calculator shows, forinstance, that July sales for rock CDs areexpected to be 23,280.

c EXERCISES

Use a graphing calculator to perform the indicated operation(s).

1. F G + F G 2. F G º F G3. 1.043F G 4. 5.08F G º 0.07F G5. MUSIC Write a matrix that gives the change in sales from May to June for

the chain of stores discussed in the example. For which categories of CDs andcassettes did sales increase from May to June? For which did sales decrease?

0.05234.15

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[A]+[B][[56 31 6 15] [53 22 9 30]]

MATRIX [A] 2X4[32 16 3 8][28 12 5 15]

2,4=15

MATRIX [A] 2X4[0 0 0 0][0 0 0 0]

Using Technology

Graphing Calculator Activity for use with Lesson 4.1ACTIVITY 4.1

.97[B][[23.28 14.5... [24.25 9.7 ...

KEYSTROKE HELP

See keystrokes for several models ofcalculators atwww.mcdougallittell.com

INT

ERNET

STUDENT HELP

MAY JUNE

R C J E R C J E

F G F G715

34

1510

2425

815

35

1612

3228

CDs

Tapes

+ , - . / 0 1 2


Multiplying Matrices

MULTIPLYING TWO MATRICES

The product of two matrices A and B is defined provided the number of columns in Ais equal to the number of rows in B.

If A is an m ª n matrix and B is ann ª p matrix, then the product ABis an m ª p matrix.

Describing Matrix Products

State whether the product AB is defined. If so, give the dimensions of AB.

a. A: 2 ª 3, B: 3 ª 4 b. A: 3 ª 2, B: 3 ª 4

SOLUTION

a. Because A is a 2 ª 3 matrix and B is a 3 ª 4 matrix, the product AB is definedand is a 2 ª 4 matrix.

b. Because the number of columns in A (two) does not equal the number of rowsin B (three), the product AB is not defined.

Finding the Product of Two Matrices

Find AB if A = F G and B = F G.

SOLUTION

Because A is a 3 ª 2 matrix and B is a 2 ª 2 matrix, the product AB is defined and is a 3 ª 2 matrix. To write the entry in the first row and first column of AB, multiplycorresponding entries in the first row of A and the first column of B. Then add. Use asimilar procedure to write the other entries of the product.

AB = F G F G

AB = F GAB = F G6

º1318

º47

º6

(º2)(3) + (3)(4)(1)(3) + (º4)(4)(6)(3) + (0)(4)

(º2)(º1) + (3)(º2)(1)(º1) + (º4)(º2)(6)(º1) + (0)(º2)

34

º1

º2

3

º40

º2

16

34

º1º2

3º4

0

º216

E X A M P L E 2

E X A M P L E 1

GOAL 1

Multiply two

matrices.

Use matrix

multiplication in real-life

situations, such as finding the

number of calories burned in

Ex. 40.

. To solve real-life

problems, such as

calculating the cost of

softball equipment in

Example 5.


GOAL 2

GOAL 1


4.2R

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• =

equal

dimensions of AB

ABm ª p

Bn ª p

Am ª n

3 4 5 6 7 8 9 :

4.2 Multiplying Matrices 209

Finding the Product of Two Matrices

If A = F G and B = F G, find each product.

a. AB b. BA

SOLUTION

a. AB = F G F G = F Gb. BA = F G F G = F G

. . . . . . . . . .

Notice in Example 3 that AB ≠ BA. Matrix multiplication is not, in general,commutative.

Using Matrix Operations

If A = F G, B = F G, and C = F G, simplify each expression.

a. A(B + C) b. AB + AC

SOLUTION

a. A(B + C) = F G 1F G + F G2A(B + C) = F G F G = F G

b. AB + AC = F G F G + F G F GA(B + C) = F G + F G = F G

. . . . . . . . . .

Notice in Example 4 that A(B + C) = AB + AC, which is true in general. This andother properties of matrix multiplication are summarized below.

611

522

45

58

26

014

12

13

13

2º1

02

º24

13

2º1

611

522

14

º17

13

2º1

12

13

02

º24

13

2º1

12

13

02

º24

13

2º1

E X A M P L E 4

24

75

20

3º1

º41

12

º104

7º1

º41

12

20

3º1

º41

12

20

3º1

E X A M P L E 3

Let A, B, and C be matrices and let c be a scalar.

ASSOCIATIVE PROPERTY OF MATRIX MULTIPLICATION A(BC ) = (AB )C

LEFT DISTRIBUTIVE PROPERTY A(B + C ) = AB + AC

RIGHT DISTRIBUTIVE PROPERTY (A + B )C = AC + BC

ASSOCIATIVE PROPERTY OF SCALAR MULTIPLICATION c(AB) = (cA)B = A(cB )

PROPERTIES OF MATRIX MULTIPLICATION

HOMEWORK HELP

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CONCEPT

SUMMARY

3 4 5 6 7 8 9 :


USING MATRIX MULTIPLICATION IN REAL LIFE

Matrix multiplication is useful in business applications because an inventory matrix,when multiplied by a cost per item matrix, results in a total cost matrix.

F G • F G = F Gm ª n n ª p m ª p

For the total cost matrix to be meaningful, the column labels for the inventory matrixmust match the row labels for the cost per item matrix.

Using Matrices to Calculate the Total Cost

SPORTS Two softball teams submit equipment lists for the season.

Each bat costs $21, each ball costs $4, and each uniform costs $30. Use matrixmultiplication to find the total cost of equipment for each team.

SOLUTION

To begin, write the equipment lists and the costs per item in matrix form. Becauseyou want to use matrix multiplication to find the total cost, set up the matrices so thatthe columns of the equipment matrix match the rows of the cost matrix.

The total cost of equipment for each team can now be obtained by multiplying theequipment matrix by the cost per item matrix. The equipment matrix is 2 3 3 and thecost per item matrix is 3 3 1, so their product is a 2 3 1 matrix.

F G F G = F G = F GThe labels for the product matrix are as follows.

TOTAL COST

Dollars

F Gc The total cost of equipment for the women’s team is $882, and the total

cost of equipment for the men’s team is $977.

882977

Women’s team

Men’s team

882977

12(21) + 45(4) + 15(30)15(21) + 38(4) + 17(30)

214

30

1517

4538

1215

E X A M P L E 5

Total costmatrix

Cost per itemmatrix

Inventorymatrix

GOAL 2

EQUIPMENT COST

Bats Balls Uniforms Dollars

F G F G214

30

Bats

Balls

Uniforms

1517

4538

1215

Women’s team

Men’s team

DOT RICHARDSON

helped lead theUnited States to the firstwomen’s softball gold medalin the 1996 Olympics byplaying shortstop.

APPLICATION LINK


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FOCUS ON

PEOPLE

Women’s team

12 bats

45 balls

15 uniforms

Men’s team

15 bats

38 balls

17 uniforms

; < = > ? @ A B


1. Complete this statement: The product of matrices A and B is defined providedthe number of

ooo

? in A is equal to the number of ooo

? in B.

2. Matrix A is 6 ª 1. Matrix B is 1 ª 2. Which of the products is defined, AB orBA? Explain.

3. Tell whether the matrix equation is true or false. Explain.

F G F G = F G F GState whether the product AB is defined. If so, give the dimensions of AB.

4. A: 3 ª 2, B: 2 ª 3 5. A: 3 ª 3, B: 3 ª 3 6. A: 3 ª 2, B: 3 ª 2

Find the product.

7. F G F G 8. f g F G 9. F G F G10. SOFTBALL EQUIPMENT Use matrix multiplication to find the total cost

of equipment in Example 5 if the women’s team needs 16 bats, 42 balls, and 16 uniforms and the men’s team needs 14 bats, 43 balls, and 15 uniforms.

MATRIX PRODUCTS State whether the product AB is defined. If so, give the

dimensions of AB.

11. A: 1 ª 3, B: 3 ª 2 12. A: 2 ª 4, B: 4 ª 3 13. A: 4 ª 2, B: 3 ª 5

14. A: 5 ª 5, B: 5 ª 4 15. A: 3 ª 4, B: 4 ª 1 16. A: 3 ª 3, B: 2 ª 4

FINDING MATRIX PRODUCTS Find the product. If it is not defined, state the

reason.

17. 3 4 F G 18. F G f g

19. F G F G 20. F G F G

21. F G F G 22. F G F G

23. F G F G 24. F G F G25. F G F G 26. F G F G46

º12

º712

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53

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0º1

3

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5

06

º2

5º1

º2º6

º44

º245

610

344

º1º2

3

0º7º1

181

137

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1.20.2

0

1.25º0.25

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º11

0º0.5

11.5

00.20.3

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1º2

08

12

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20

43

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º23

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40

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13

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03.2

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}}12

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0º1

1º2

3º2º1

º330

º2º3

4403

21

0º1

1º2

35

5º3

01

20

01

20

35

5º3

GUIDED PRACTICE


Concept Check ✓

Skill Check ✓


STUDENT HELP

STUDENT HELP

HOMEWORK HELP

Example 1: Exs. 11–16Examples 2, 3: Exs. 17–26Example 4: Exs. 27–32Example 5: Exs. 35–40

; < = > ? @ A B


SIMPLIFYING EXPRESSIONS Using the given matrices, simplify the

expression.

A = F G, B = F G, C = F G, D = F G, E = F G27. 2AB 28. AB + AC 29. D(D + E)

30. (E + D)E 31. º3(AC) 32. 0.5(AB) + 2AC

SOLVING MATRIX EQUATIONS Solve for x and y.

33. F G F G = F G 34. F G F G = F GAGRICULTURE In Exercises 35 and 36, use the following information.

The percents of the total 1997 world production of wheat, rice, and maize are shown in the matrix for the four countries that grow the most grain: China, India, the Commonwealth of Independent States (formerly the Soviet Union), and the United States. The total 1997 world production (in thousands of metric tons) of wheat, rice, and maize is 608,846, 570,906, and 586,923, respectively.

c Source: Food and Agriculture Organization of the United Nations

35. Rewrite the matrix to give the percents as decimals.

36. Show how matrix multiplication can be used to determine how many metric tonsof all three grains were produced in each of the four countries.

CLASS DEBATE In Exercises 37º39, use the

following information.

Three teams participated in a debating competition. The final score for each team is based on how many students ranked first, second, and third in a debate. The results of 12 debates are shown in matrix A.

37. Teams earn 6 points for each first place, 5 points for each second place, and 4 points for each third place. Organize this information into a matrix B.

38. Find the product AB.

39. LOGICAL REASONING Which team won the competition? How many pointsdid the winning team score?

40. EXERCISE The numbers of calories burned by people of different weights doing different activities for 20 minutes are shown in the matrix. Show how matrix multiplication can be used to write the total number of calories burned by a 120 pound person and a 150 pound person who each bicycled for 40 minutes, jogged for 10 minutes, and then walked for 60 minutes.

c Source: Medicine and Science in Sports and Exercise

511

yº13

º214

92

º1

31

1x

4º2

619

y

1x3

244

12

º2

º230

62

º4

541

º2º1

3

143

º22

º3

3º1º2

31

º1º2

04

1º2

º2º1

46

MATRIX A

1st 2nd 3rd

F G452

526

354

Team 1

Team 2

Team 3

GRAIN PRODUCTION

Wheat Rice Maize

3 418%

1.7%0.5%

40.5%

34.8%21.5%0.1%1.4%

20.1%22%

7.3%11.3%

China

India

C.I.S.

U.S.

EXERCISE

A 120 pound personwalking at a moderate paceof 3 mi/h would burn about64 Cal in 20 min. At a briskpace of 4.5 mi/h, the personwould burn about 82 Cal in20 min.

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CALORIES BURNED

120 lb 150 lb

person person

F G13615979

10912764

Bicycling

Jogging

Walking

DATA UPDATE

Visit our Web sitewww.mcdougallittell.com

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STUDENT HELP

C D E F G H I J41. Writing Describe the process you use when multiplying any two matrices.

42. MULTIPLE CHOICE What is the product of F G and F G?

¡A F G ¡B F G ¡C F G ¡D F G43. MULTIPLE CHOICE If A is a 2 ª 3 matrix and B is a 3 ª 2 matrix, what are the

dimensions of BA?

¡A 2 ª 2 ¡B 3 ª 3 ¡C 3 ª 2 ¡D 2 ª 3 ¡E BA not defined

44. ROTATIONAL MATRIX Matrix A is a 90° rotational matrix. Matrix B containsthe coordinates of the triangle’s vertices shown in the graph.

A = F G B = F Ga. Calculate AB. Graph the coordinates of the

vertices given by AB. What rotation does AB represent in the graph?

b. Find the 180° and 270° rotations of the original triangle by using repeated multiplication of the 90° rotational matrix. What are the coordinates of the vertices of the rotated triangles?

CALCULATING AREA Find the area of the figure. (Skills Review, p. 914)

45. 46. 47.

WRITING EQUATIONS Write an equation of the line with the given properties.

(Review 2.4)

48. slope: }12

}, passes through (1, 8) 49. slope: º}14

}, passes through (0, 4)

50. passes through (3, º6) and (2, 10) 51. passes through (1, 5) and (4, 14)

52. x-intercept: º7, y-intercept: º5 53. x-intercept: 4, y-intercept: º6

SOLVING SYSTEMS Solve the system of linear equations using any algebraic

method. (Review 3.2 for 4.3)

54. 4x + y = 6 55. 2x + y = º9 56. º9x + 5y = 1º3x º 2y = 8 3x + 5y = 4 3x º 2y = 2

57. 2x º 2y = 8 58. º3x + 4y = º1 59. 5x + 2y = º10x º y = 1 6x + 2y = 7 º3x º 8y = 40

60. 7x + 3y = 11 61. 5x º 4y = º1 62. ºx + 7y = º49º2x + 5y = 32 2x º 9y = 10 12x + y = º24

3 ft

6 m

4 m

15 m

12 m

MIXED REVIEW

º42

º48

º74

º10

01

08

1º30

08

1º26

06

8º30

0º24

2º26

º20

7º1

º1º2

0º4


TestPreparation

★★Challenge

2 K K LM

(24, 8)

(24, 2)

(27, 4)

EXTRA CHALLENGE


C D E F G H I JDeterminants

and Cramer’s Rule

EVALUATING DETERMINANTS

Associated with each square matrix is a real number called its The determinant of a matrix A is denoted by det A or by |A|.

Evaluating Determinants

Evaluate the determinant of the matrix.

a. F G b. F GSOLUTION

a. * * = 1(5) º 2(3) = 5 º 6 = º1

b. * * = [0 + (º1) + (º12)] º (0 + 4 + 8) = º13 º 12

= º25

. . . . . . . . . .

You can use a determinant to find the area of a triangle whose vertices are points in acoordinate plane.

º102

2º2

1

314

º102

2º2

1

35

12

314

º102

2º2

1

35

12

E X A M P L E 1

determinant.

GOAL 1


Evaluate

determinants of 2 ª 2 and

3 ª 3 matrices.

Use Cramer’s rule

to solve systems of linear

equations, as applied in

Example 5.

. To solve real-lifeproblems, such as finding the

area of the Golden Triangle of

India in Ex. 58.


GOAL 2

GOAL 1


4.3R

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DETERMINANT OF A 2 ª 2 MATRIX

det F G = * * = ad º cb

DETERMINANT OF A 3 ª 3 MATRIX

det F G = * * = (aei + bfg + cdh) º (gec + hfa + idb)

b

e

h

a

d

g

c

f

i

b

e

h

a

d

g

c

f

i

b

e

h

a

d

g

b

d

a

c

b

d

a

c

THE DETERMINANT OF A MATRIX

Subtract the sum of the products in red

from the sum of the products in blue.

2

The determinant of a 2 ª 2 matrix is the difference

of the products of the entries on the diagonals.

Repeat the first two columns

to the right of the

determinant.

1

N O P Q R S T U

The Area of a Triangle

The area of the triangle shown is:

Area = ±}

12}* *

= ±}

12}[(0 + 12 + 8) º (0 + 2 + 8)] = 5

The Area of a Triangular Region

BERMUDA TRIANGLE The Bermuda Triangle is a large triangular region in the Atlantic Ocean. Many ships and airplanes have been lost in this region. The triangle is formed by imaginary lines connecting Bermuda, Puerto Rico, and Miami, Florida. Use a determinant to estimate the area of the Bermuda Triangle.

SOLUTION

The approximate coordinates of the Bermuda Triangle’s three vertices are (938, 454), (900, º518), and (0, 0). So, the area of the region is as follows:

Area = ±}

12}* *

= ±}

12} [(º485,884 + 0 + 0) º (0 + 0 + 408,600)]

= 447,242

c The area of the Bermuda Triangle is about 447,000 square miles.

111

454º518

0

938900

0

E X A M P L E 3

111

202

146

E X A M P L E 2

4.3 Determinants and Cramer's Rule 215

VV W X(1, 2) (6, 2)

(4, 0)

Bermuda(938, 454)

Puerto Rico(900, 2518)

Miami (0, 0)

Each tick markrepresents 200 mi.

YZ [\

The area of a triangle with vertices

(x1, y1), (x2, y2), and (x3, y3) is given by

Area = ±}

12

}* *where the symbol ± indicates that the

appropriate sign should be chosen to

yield a positive value.

1

1

1

y1

y2

y3

x1

x2

x3

AREA OF A TRIANGLE

XW

(x1, y1)

(x2, y2)

(x3, y3)

BERMUDA

TRIANGLE

The U.S.S. Cyclops, shownabove, disappeared in theBermuda Triangle in March,1918.

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N O P Q R S T U

* *5º4

2º10


USING CRAMER’S RULE

You can use determinants to solve a system of linear equations. The method, called and named after the Swiss mathematician Gabriel Cramer(1704º1752), uses the of the linear system.

LINEAR SYSTEM COEFFICIENT MATRIX

ax + by = ecx + dy = f

In Cramer’s rule, notice that the denominator for x and y is the determinant of thecoefficient matrix of the system. The numerators for x and y are the determinants of the matrices formed by using the column of constants as replacements for thecoefficients of x and y, respectively.

Using Cramer’s Rule for a 232 System

Use Cramer’s rule to solve this system:

SOLUTION

Evaluate the determinant of the coefficient matrix.

* * = º32 º 10 = º42

Apply Cramer’s rule since the determinant is not 0.

x = }º42} = }º8 º

º4(2º50)} = }º

4422} = º1

y = }º42} = }º8º04º2

4} = }ºº

84

42} = 2

c The solution is (º1, 2).

✓CHECK Check this solution 8(º1) + 5(2) · 2 2(º1) º 4(2) · º10in the original equations. 2 = 2 ✓ º10 = º10 ✓

5º4

82

8x + 5y = 22x º 4y = º10

E X A M P L E 4

coefficient matrix

Cramer’s rule

GOAL 2

F Gbd

ac

Let A be the coefficient matrix of this linear system:

ax + by = e

cx + dy = f

If det A ≠ 0, then the system has exactly one solution. The solution is:

x = }det A

} and y = }det A

}

CRAMER’S RULE FOR A 2 X 2 SYSTEM

* *b

d

e

f * *e

f

a

c

* *2º10

82

HOMEWORK HELP


INT

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STUDENT HELP

] ^ _ ` a b c d

CHEMIST

Chemists researchand put to practical useknowledge about chemicals.Research on the chemistry ofliving things sparks advancesin medicine, agriculture, andother fields.

CAREER LINK


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CAREERS


Using Cramer’s Rule for a 3 ª3 System

SCIENCE CONNECTION The atomicweights of three compounds are shown.Use a linear system and Cramer’s rule tofind the atomic weights of carbon (C),hydrogen (H), and oxygen (O).

SOLUTION

Write a linear system using the formula for each compound. Let C, H, and Orepresent the atomic weights of carbon, hydrogen, and oxygen.

C + 4H = 163C + 8H + 3O = 92

2H + O = 18

Evaluate the determinant of the coefficient matrix.

* * = (8 + 0 + 0) º (0 + 6 + 12) = º10

Apply Cramer’s rule since the determinant is not 0.

C = }º10} = }ºº11200

} = 12 Atomic weight of carbon

H = }º10} = }ºº1100} = 1 Atomic weight of hydrogen

O = }º10} = }ºº11600

} = 16 Atomic weight of oxygen

c The weights of carbon, hydrogen, and oxygen are 12, 1, and 16, respectively.

031

482

130

E X A M P L E 5

Let A be the coefficient matrix of this linear system:

ax + by + cz = j

dx + ey + fz = k

gx + hy + iz = l

If det A ≠ 0, then the system has exactly one solution. The solution is:

x = }det A

}, y = }det A

}, and z = }det A

}

CRAMER’S RULE FOR A 3 X 3 SYSTEM

Compound Formula Atomic weight

Methane CH4 16

Glycerol C3H8O3 92

Water H2O 18

* *c

f

i

b

e

h

j

k

l * *c

f

i

j

k

l

a

d

g * *j

k

l

b

e

h

a

d

g

* *031

169218

130

* *169218

482

130

* *031

482

169218

e f g h i j k l1. Explain Cramer’s rule and how it is used.

2. Can two different matrices have the same determinant? If so, give an example.

3. ERROR ANALYSIS Find the error in each calculation.a. b.

4. To use Cramer’s rule to solve a linear system, what must be true of thedeterminant of the coefficient matrix?


5. F G 6. F G 7. F GUse Cramer’s rule to solve the linear system.

8. 6x º 8y = 4 9. 2x + 7y = º3 10. 12x º 2y = 24x º 5y = º4 3x º 8y = º23 º14x + 11y = 51

11. SCHOOL SPIRIT You are making a large pennant for your school football team. A diagram of the pennant is shown at the right. The coordinates given are measured in inches. How many square inches of material will you need to make the pennant?

2 ª 2 DETERMINANTS Evaluate the determinant of the matrix.

12. F G 13. F G 14. F G15. F G 16. F G 17. F G18. F G 19. F G 20. F G3 ª 3 DETERMINANTS Evaluate the determinant of the matrix.

21. F G 22. F G 23. F G24. F G 25. F G 26. F G27. F G 28. F G 29. F Gº10

6º14

402

15º10º8

201812

29

15

º3º10

11

º10

º2

1296

310

º5

994

23

13

8123

º192

085

º400

º22

º4

1641

1207

2º4º1

5134

010

º5

411

º921

540

º121

438

12º2

5

28

12º5

º310

08

59

º6º3

89

15

04

4º3

112

º7º7

31

9º2

03

8º1

2º2

º45


º24

8º2

4º1

º15

12

06

GUIDED PRACTICE


Vocabulary Check ✓Concept Check ✓

Skill Check ✓

STUDENT HELP

HOMEWORK HELP

Example 1: Exs. 12–29Example 2: Exs. 30–35Example 3: Exs. 54–58Example 4: Exs. 36–44,

59Example 5: Exs. 45–53,

60


STUDENT HELP

* * = 6 º 5 = 1 * * = º2 º 12 = º1423

4º1

º12

35

m no n GO TEAM

pq(0, 50)

(70, 20)

(0, 0)

e f g h i j k l

SAILING Theedges of a sail are

called the luff, leech, andfoot. The luff length of the jibis usually 80% to 90% of thedistance from the deck tothe head of the jib.

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APPLICATIONS

leech luff

foot mainsail jib

head


AREA OF A TRIANGLE Find the area of the triangle with the given vertices.

30. A(0, 1), B(2, 7), C(5, 5) 31. A(3, 6), B(3, 0), C(1, 3)

32. A(6, º1), B(2, 2), C(4, 8) 33. A(º4, 2), B(3, º1), C(º2, º2)

34. A(2, º6), B(º1, º4), C(0, 2) 35. A(1, 3), B(º2, 6), C(º1, 1)

USING CRAMER’S RULE Use Cramer’s rule to solve the linear system.

36. 2x + y = 3 37. 7x º 5y = 11 38. 9x + 2y = 75x + 6y = 4 3x + 10y = º56 4x º 3y = 42

39. x + 7y = º3 40. ºx º 12y = 44 41. 4x º 3y = 183x º 5y = 17 12x º 15y = º51 8x º 7y = 34

42. 4x º 5y = 13 43. 8x º 9y = 32 44. 3x + 10y = 502x º 7y = 24 º5x + 7y = 40 12x + 15y = 64

SOLVING SYSTEMS Use Cramer’s rule to solve the linear system.

45. x + 2y º 3z = º2 46. x + 3y º z = 1 47. 3x + 2y º 5z = º10x º y + z = º1 º2x º 6y + z = º3 6x º z = 83x + 4y º 4z = 4 3x + 5y º 2z = 4 ºy + 3z = º2

48. x + 2y + z = 9 49. 4x + y + 6z = 7 50. x + 4y º z = º7x + y + z = 3 3x + 3y + 2z = 17 2x º y + 2z = 155x º 2z = º1 ºx º y + z = º9 º3x + y º 3z = º22

51. 2x + y + z = 5 52. ºx + 2y + 7z = 13 53. º3x + y + 2z = º14x + 4y º 2z = 9 2x º y º 2z = º2 9x º y + 2z = º86x + 5y = 16 3x + 5y + 2z = º14 8x + 5y º 4z = 6

54. BIRDS Black-necked stilts are birds that live throughoutFlorida and surrounding areas but breed mostly in the triangularregion shown on the map. Estimate the area of this region.The coordinates given aremeasured in miles.

SAILING In Exercises 55–57,

use the following information.

On a Marconi-rigged sloop, there are two triangular sails, a mainsail and a jib. These sails are shown in acoordinate plane at the right. The coordinates in the plane are measured in feet.

55. Find the area of the mainsail shown.

56. Find the area of the jib shown.

57. Suppose you are making a scale modelof the sailboat with the sails shownusing a scale of l in. = 6 ft. What is thearea of the model’s mainsail?

r rs ts rs u

rrr v w

xmainsail jib

(35, 220)

(0, 0)

(112, 56)

yz {|Each tick mark

represents 50 miles.

} ~ � � � � � �58. The Golden

Triangle refers to a large triangular regionin India. The Taj Mahal is one of the many wonders that lie within the boundaries of this triangle. The triangle is formed by imaginary lines that connect the cities of New Delhi, Jaipur, and Agra. Use the coordinates on the map and a determinant to estimate the area of the Golden Triangle. The coordinates given are measured in miles.

59. BUYING GASOLINE You fill up your car with 10 gallons of premiumgasoline and fill a small gas can with 2 gallons of regular gasoline for your lawnmower. You pay the cashier $13.56. The price of premium gasoline is 12 centsmore per gallon than the price of regular gasoline. Use a linear system andCramer’s rule to find the price per gallon for regular and premium gasoline.

60. The atomic weights of three compounds are shown.

Use a linear system and Cramer’s rule to find the atomic weights of sulphur (S),nitrogen (N), and flourine (F).

61. LOGICAL REASONING Explain what happens to the determinant of a matrixwhen you switch two rows or two columns.

QUANTITATIVE COMPARISON In Exercises 62 and 63, choose the statement

that is true about the given quantities.

¡A The quantity in column A is greater.

¡B The quantity in column B is greater.

¡C The two quantities are equal.

¡D The relationship cannot be determined from the given information.

62.

63.

64. DETERMINANT RELATIONSHIPS Let A = F G and B = F G.

a. How is det AB related to det A and det B?

b. How is det kA related to det A if k is a constant? Check your answer usingmatrix B and several other 2 ª 2 matrices.

5º4

3º2

º12

23

SCIENCE CONNECTION

SOCIAL STUDIES CONNECTION


TestPreparation

★★Challenge

Column A Column B

The area of a triangle with vertices The area of a triangle with vertices (º3, 4), (4, 2), and (1, º2) (4, 2), (1, º2), and (3, º4)

det F G det F G15

º73

610

º5º2

Compound Formula Atomic weight

Tetrasulphur tetranitride S4N4 184

Sulphur hexaflouride SF6 146

Dinitrogen tetraflouride N2F4 104

EXTRA CHALLENGE


New Delhi(100, 120)

Jaipur(0, 0)

Agra(140, 20)

Each tick markrepresents 20 miles.

��

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EVALUATING FUNCTIONS Find the indicated value of ƒ(x). (Review 2.1)

65. ƒ(x) = x º 10, f (7) 66. ƒ(x) = 3x + 7, ƒ(º2)

67. ƒ(x) = ºx2 + 5, ƒ(º1) 68. ƒ(x) = x2 º 2x º 4, ƒ(7)

69. ƒ(x) = x2 + 4x º 1, ƒS}

12}D 70. ƒ(x) = x5 º 2x º 10, ƒ(3)

GRAPHING SYSTEMS Graph the system of linear inequalities. (Review 3.3)

71. x < 3 72. y ≥ 2x º 3 73. y > ºx º 5x > º2 y > º5x º 8 y > 3x + 1

74. x + y > 3 75. 2x º y ≥ 2 76. 4x º 3y > 14x + y < 4 5x º y ≥ 2 ºx + y ≥ 4

MULTIPLYING MATRICES Find the product. (Review 4.2 for 4.4)

77. F G F G 78. F G F G 79. F G F G80. F G F G 81. F G F G 82. F G F G

Perform the indicated operation(s). (Lessons 4.1, 4.2)

1. F G + F G 2. F G º F G3. º2F G + 2F G 4. F G º 4F G5. F G F G 6. F G F G

Evaluate the determinant of the matrix. (Lesson 4.3)

7. F G 8. F G 9. F G 10. F GUse Cramer’s rule to solve the linear system. (Lesson 4.3)

11. º8x + y = º6 12. 3x º 2y = 10 13. 5x + 4y = 12º5x + 4y = 3 º6x + y = º7 3x º 6y = 3

14. 4x + y + 6z = 2 15. x + y + 4z = 7 16. 3x + 3y º 2z = º182x + 2y + 4z = 1 2x º 3y º z = º24 º5x º 2y º 3z = º1ºx º y + z = º5 º4x + 2y + 2z = 8 7x + y + 6z = 14

17. GARDENING You are planning to turn a triangular region of your yard into a garden. The vertices of the triangle are (0, 0), (5, 2), and (3, 6) where thecoordinates are measured in feet. Find the area of the triangular region. (Lesson 4.3)

º63

º3

520

1221

3º2

1

208

º156

º3º2

96

32

º4º6

0º3º6

194

30

º14

22

70

3º2

º1º2

86

º3º5

1

º160

20

º2

1005

º66

º4

439

º33

6º5

º29

74

7º1

º35

0º2

º85

5º7

º1º8

º3º2

108

5º6

º24

QUIZ 1 Self-Test for Lessons 4.1–4.3

61.9

1.6º4

1.3º3

º21.5

0.60.8

04

31

0.50.2

916

1012

º52

3º7

3º1

º88

º24

110

º38

04

º1º10

74

º1º3

63

º41

º25

MIXED REVIEW

} ~ � � � � � �Developing Concepts

ACTIVITY 4.4Group Activity for use with Lesson 4.4

GROUP ACTIVITY

Work with a partner.

MATERIALS

• pencil

• paper

Investigating Identity and Inverse Matrices

c QUESTION What are some properties of identity and inverse matrices?

c EXPLORING THE CONCEPT

Let A = F G, B = F G, and C = F G. Consider the 2 ª 2

identity matrix I = F G. Find AI, BI, and CI. What do you notice?

Find IA, IB, and IC using the matrices from Step 1. Is multiplication by theidentity matrix commutative?

Let D = F G. The inverse of D is E = F G. Find DE and ED.

What do you notice?

Use matrix multiplication to decide which of the following is the inverse of the

matrix A in Step 1: F G, F G, or F G.

c DRAWING CONCLUSIONS

1. For any 2 ª 2 matrix A, what is true of the products AI and IA where I is the2 ª 2 identity matrix? Justify your answer mathematically.

(Hint: Let A = F G, and compute AI and IA.)

2. How is the relationship between I = F G and other 2 ª 2 matrices similar

to the relationship between 1 and other real numbers?

3. What do you think is the identity matrix for the set of 3 ª 3 matrices? Checkyour answer by multiplying your proposed identity matrix by several 3 ª 3matrices.

4. What is the relationship between a matrix, its inverse, and the identity matrix?How is this relationship like the one that exists between a nonzero real number,its reciprocal, and 1?

5. Does every nonzero matrix have an inverse? Explain. (Hint: Consider a 2 ª 2matrix whose first row contains all nonzero entries and whose second rowcontains all zero entries.)

6. Find the inverse of F = F G by finding values of a, b, c, and d such that

F G F G = F G.01

10

b

d

a

c

74

21

74

21

01

10

b

d

a

c

2º5

º13

3º1

º52

º31

5º2

4

º57

3º4

53

74

3

2

01

10

0.80.3

0.10.6

06

º4º7

35

12

1


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4.4 Identity and Inverse Matrices 223

Identity and Inverse Matrices

USING INVERSE MATRICES

The number 1 is the multiplicative identity for real numbers because 1 • a = a anda • 1 = a. For matrices, the n ª n is the matrix that has 1’s on themain diagonal and 0’s elsewhere.

2 ª 2 IDENTITY MATRIX 3 ª 3 IDENTITY MATRIX

I = F G I = 3 4If A is any n ª n matrix and I is the n ª n identity matrix, then IA = A and AI = A.

Two n ª n matrices are of each other if their product (in both orders) is then ª n identity matrix. For example, matrices A and B below are inverses of each other.

AB = F G F G = F G = I BA = F G F G = F G = I

The symbol used for the inverse of A is Aº1.

Finding the Inverse of a 2 32 Matrix

Find the inverse of A = F G.

SOLUTION

Aº1 = }6 º

14

} F G = }

12

}F G = 3 4✓CHECK You can check the inverse by showing that AAº1 = I = Aº1A.

F G 3 4 = F G and 3 4 F G = F G01

10

12

34

º}

21

}

}

32

}

1

º2

01

10

º}

21

}

}

32

}

1

º2

12

34

º}

21

}

}

32

}

1

º2

º13

2º4

º13

2º4

12

34

E X A M P L E 1

01

10

º12

3º5

13

25

01

10

13

25

º12

3º5

inverses

001

010

100

01

10

identity matrix

GOAL 1

Find and use

inverse matrices.

Use inverse

matrices in real-life

situations, such as encoding

a message in Example 5.

. To solve real-life

problems, such as decoding

names of landmarks in

Exs. 44–48.


GOAL 2

GOAL 1


4.4R

EAL LIFE

REA

L LIFEThe inverse of the matrix A = 3 4 is

Aº1 = }

|A

1|

} 3 4 = }ad º

1cb

} 3 4 provided ad º cb ≠ 0.ºb

a

d

ºc

ºb

a

d

ºc

b

d

a

c

THE INVERSE OF A 2 X 2 MATRIX

Look Back For help with multiplicativeinverses of real numbers,see p. 5.

STUDENT HELP

The artist Jim Sanborn uses

cryptograms in his work,

such as Kryptos above.

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Solving a Matrix Equation

Solve the matrix equation AX = B for the 2 ª 2 matrix X.

A B

F GX = F GSOLUTION

Begin by finding the inverse of A.

Aº1 = }4 º

13

} F G = F GTo solve the equation for X, multiply both sides of the equation by Aº1 on the left.

F G F GX = F G F G Aº1AX = Aº1B

F GX = F G IX = Aº1B

X = F G X = Aº1B

✓CHECK You can check the solution by multiplying A and X to see if you get B.

. . . . . . . . . .

Some matrices do not have an inverse. You can tell whether a matrix has an inverseby evaluating its determinant. If det A = 0, then A does not have an inverse. Ifdet A ≠ 0, then A has an inverse.

The inverse of a 3 ª 3 matrix is difficult to compute by hand. A calculator that willcompute inverse matrices is useful in this case.

Finding the Inverse of a 3 33 Matrix

Use a graphing calculator to find the inverse of A. Then use the calculator to

verify your result.

A = F GSOLUTION

Enter the matrix A into the graphing calculator and calculate Aº1. Then computeAAº1 and Aº1A to verify that you obtain the 3 ª 3 identity matrix.

0º1º3

º10

º2

116

E X A M P L E 3

º2º3

20

º2º3

20

01

10

º53

8º6

14

13

º11

4º3

14

13

14

13

14

13

º53

8º6

º11

4º3

E X A M P L E 2

[A]-1

[[-2 -3 1]

[-3 -3 1]

[-2 -4 1]]

[A][A]-1

[[1 0 0]

[0 1 0]

[0 0 1]]

[A]-1[A]

[[1 0 0]

[0 1 0]

[0 0 1]]

HOMEWORK HELP


INT

ERNET

STUDENT HELP

KEYSTROKE HELP

Visit our Web sitewww.mcdougallittell.comto see keystrokes forseveral models ofcalculators.

INT

ERNET

STUDENT HELP

� � � � � � � �


USING INVERSE MATRICES IN REAL LIFE

A cryptogram is a message written according to a secret code. (The Greek wordkruptos means hidden and the Greek word gramma means letter.) The followingtechnique uses matrices to encode and decode messages.

First assign a number to each letter in the alphabet with 0 assigned to a blank space.

__ = 0 E = 5 J = 10 O = 15 T = 20 Y = 25

A = 1 F = 6 K = 11 P = 16 U = 21 Z = 26

B = 2 G = 7 L = 12 Q = 17 V = 22

C = 3 H = 8 M = 13 R = 18 W = 23

D = 4 I = 9 N = 14 S = 19 X = 24

Then convert the message to numbers partitioned into 1 ª 2 uncoded row matrices.

To encode a message, choose a 2 ª 2 matrix A that has an inverse and multiply theuncoded row matrices by A on the right to obtain coded row matrices.

Converting a Message

Use the list above to convert the message GET HELP to row matrices.

SOLUTION

G E T __ H E L P

f gf gf gf g

Encoding a Message

CRYPTOGRAPHY Use A = F G to encode the message GET HELP.

SOLUTION

The coded row matrices are obtained by multiplying each of the uncoded rowmatrices from Example 4 by the matrix A on the right.

c The coded message is 9, 11, 40, 60, 11, 14, 8, 4.

3º2

2º1

E X A M P L E 5

16125802057

E X A M P L E 4

GOAL 2

NAVAJO CODE

During World War II,a Marine Corps code basedon the complex Navajolanguage was used to sendmessages.

APPLICATION LINK


INT

ERNET

RE

AL LIFE

RE

AL LIFE

FOCUS ON

APPLICATIONS

RE

AL LIFE

RE

AL LIFE

Cryptography

UNCODED ENCODING CODED ROW

ROW MATRIX MATRIX A MATRIX

f7 5g F G = [9 11]

f20 0g F G = [40 60]

f8 5g F G = [11 14]

f12 16g F G = [8 4]3

º22

º1

3º2

2º1

3º2

2º1

3º2

2º1

� � � � � � � �


DECODING USING MATRICES Decoding the cryptogram created in Example 5would be difficult for people who do not know the matrix A. When larger codingmatrices are used, decoding is even more difficult. But for an authorized receiver whoknows the matrix A, decoding is simple. The receiver only needs to multiply thecoded row matrices by Aº1 on the right to retrieve the uncoded row matrices.

Decoding a Message

CRYPTOGRAPHY Use the inverse of A = F G to decode this message:

º4, 3, º23, 12, º26, 13, 15, º5, 31, º5, º38, 19, º21, 12, 20, 0, 75, º25

SOLUTION

First find Aº1: Aº1 = }3 º

12

} F G = F GTo decode the message, partition it into groups of two numbers to form coded rowmatrices. Then multiply each coded row matrix by Aº1 on the right to obtain theuncoded row matrices.

From the uncoded row matrices you can read the message as follows.

f gf gf gf gf gf gf gf gf gB E A M __ M E __ U P __ S C O T T Y __

025202015319016210513013152

13

12

13

12

º11

3º2

E X A M P L E 6

ALAN TURING,

an English mathema-tician, helped break codesused by the German militaryduring World War II.

RE

AL LIFE

RE

AL LIFE

FOCUS ON

PEOPLE

CODED ROW DECODING UNCODED

MATRIX MATRIX Aº1 ROW MATRIX

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g

f g F G = f g02513

12

º2575

202013

12

020

15313

12

12º21

19013

12

19º38

162113

12

º531

0513

12

º515

13013

12

13º26

13113

12

12º23

5213

12

3º4

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1. What is the identity matrix for 2 ª 2 matrices? for 3 ª 3 matrices?

2. For two 2 ª 2 matrices A and B to be inverses of each other, what must be trueof AB and BA?

3. Explain how to find the inverse of a 2 ª 2 matrix.

4. How do you know that the matrix X in Example 2 must be 2 ª 2?

5. If B = F G, does B have an inverse? Explain.

Find the inverse of the matrix.

6. F G 7. F G 8. F G9. F G 10. F G 11. F G

12. DECODING A MESSAGE Use the coding information on pages 225 and226 and the inverse of the matrix D to decode the following message.

D = F G º71, 39, º35, 20, º118, 69, º84, 49, º95, 57

FINDING INVERSES Find the inverse of the matrix.

13. F G 14. F G 15. F G16. F G 17. F G 18. F G19. F G 20. F G 21. F G22. F G 23. 3 4 24. 3 4SOLVING EQUATIONS Solve the matrix equation.

25. F GX = F G 26. F GX = F G27. F GX = F G 28. F GX = F G29. F GX + F G = F G 30. F GX + F G = F G31. F GX º F G = F G 32. F GX º F G = F G6

248

17

º15

º3º2

46

º2º1

31

10

23

26

º1º4

9º6

16

4º3

34

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º74

º3º9

7º2

515

81

74

31

18º13

º5º3

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º31

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65

0º1

43

41

20

2020

1726

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58

10

3º4

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}

43

}

}

52

}

}

54

}

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2.510

2.28

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21

}

1

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23

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11º9

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5º4

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21

73

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87

11

23

68

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4º3


31

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20.2

1.63.2

34

0.52.5

4

}

14

}

}

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}

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04

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2º1

º30

32

º4º3

º41

8º2

GUIDED PRACTICE

Vocabulary Check ✓Concept Check ✓

Skill Check ✓


STUDENT HELP

STUDENT HELP

HOMEWORK HELP

Example 1: Exs. 13–24, 33Example 2: Exs. 25–32Example 3: Exs. 34–39Examples 4, 5: Exs. 40–43Example 6: Exs. 44–48

� � � � � � � �


IDENTIFYING INVERSES Tell whether the matrices are inverses of each other.

33. F G and F G 34. F G and F G35. F G and F G 36. F G and F G

FINDING INVERSES Use a graphing calculator to find the inverse of the

matrix A. Check the result by showing that AAº1 = I and Aº1

A = I.

37. A = F G 38. A = F G 39. A = F GENCODING Use the code on page 225 and the matrix to encode the message.

40. JOB WELL DONE 41. STAY THERE

A = F G A = F G42. COME TO DINNER 43. HAPPY BIRTHDAY

A = F G A = F GTRAVEL In Exercises 44–48, use the following

information.

Your friend is traveling abroad and is sending youpostcards with encoded messages. You must decipherwhat landmarks your friend has visited. Use the inverseof matrix D to decode each message. Each messagerepresents a landmark in the country where your friendis traveling. Use the coding information on pages 225and 226 to help you.

D = F G44. º1, 4, 30, º41, 39, º58, 22, º33, 31, º46, 23, º34, 1, 1

45. 21, º31, 22, º26, º9, 19, º20, 40, º3, 11, 20, º24, 10, º15

46. 39, º58, º2, 12, 0, 9, º19, 38, 13, º9, º16, 33, 10, º15

47. 32, º44, 10, º15, º4, 15, 9, º13, 40, º60, 22, º25, 7, º6, 4, 6

48. Using the decoded messages, tell what country your friend is visiting.

49. Use the matrices shown. The columns of matrix T givethe coordinates of the vertices of a triangle. Matrix A is a transformation matrix.

A = F G T = F Ga. Find AT and AAT. Then draw the original triangle and the two transformed

triangles. What transformation does A represent?

b. Suppose you start with the triangle determined by AAT and want to reverse thetransformation process to produce the triangle determined by AT and then thetriangle determined by T. Describe how you can do this.

32

24

11

º10

01

GEOMETRY CONNECTION

º32

2º1

º22

5º4

º11

4º3

23

11

º25

1º2

º208

133

254

º63

º9

01

º3

º7º411

502

452

º315

502

452

3º2

1

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23

21

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104

º9

213

º42

º5

304

º8º3

6

21

º1

114

º8

8º5

º10

º107

12

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º134

223

057

3º10

13

º3º1

103

Skills Review For help withtransformations, see p. 921.

STUDENT HELP

� � � � � � � �


50. Writing Describe the process used to solve a matrix equation.

51. MULTIPLE CHOICE What is the inverse of F G?

¡A 3 4 ¡B F G ¡C 3 4 ¡D F G52. MULTIPLE CHOICE What is the solution of F GX = F G?

¡A F G ¡B F G ¡C F G ¡D F G ¡E F G53. CODE BREAKER You are a code breaker and intercept the encoded message

45, º35, 38, º30, 18, º18, 35, º30, 81, º60, 42, º28, 75, º55, 2, º2, 22,º21, 15, º10 that you know is being sent to someone named John. You canconclude that f gAº1 = f g and f gAº1 = f gwhere Aº1 is the inverse of the encoding matrix A, 10 represents J, 15 representsO, 8 represents H, and 14 represents N.

Let Aº1 = F G.

a. Write and solve two systems of equations to find w, x, y, and z.

b. Find Aº1, and decode the rest of the message.

SOLVING SYSTEMS Solve the system of linear equations using any algebraic

method. (Review 3.2, 3.6 for 4.5)

54. 3x + 5y = 12 55. 4x º 12y = 2 56. º5x + 7y = 33x + 4y = 11 º2x + 6y = º1 4x º 9y = º40

57. 7x + y + 3z = 22 58. x + 3z = 6 59. 2x + y º 4z = 42x º 2y + 9z = º10 º2x + 3y + z = º11 4x º 3y + 8z = º8º3x º 5y º 10z = 8 3x º y + 2z = 13 º2x + 7y º 12z = 24

MATRIX OPERATIONS Perform the indicated operation, if possible. If not

possible, state the reason. (Review 4.1)

60. F G + F G 61. F G º F G62. º8F G 63. F G º F G64. F G + F G 65. }

12

}F G66. CATERING You are in charge of catering for a school function. To limit the cost,

you will serve only two entrees. One is a vegetarian dish that costs $6 and the other isa chicken dish that costs $8. If there will be 150 people at the function and yourbudget for the food is $1000, how many of each type of entree will be served?(Review 3.1, 3.2)

216

108

46

º1º9

48

3º2

º14

º25

6º3

9º15

º2º12

º10º9

816

º513

7º9

40

38

º1º6

º53

º3º1

º22

º65

8º2

º30

4º2

2º1

º4º5

MIXED REVIEW

x

z

w

y

148º30381510º3545

72

04

47

02

24

07

74

0º2

74

02

4325

42

21

53

1

º1

3

º}

72

}

º}

113}

}

113}

}

133}

º}

276}

1

1

º3

º}

72

}

º}

113}

º}

113}

}

133}

}

276}

º26

º27

TestPreparation

★★Challenge

EXTRA CHALLENGE


� � � � � � � �


Solving Systems Using Inverse Matrices

SOLVING SYSTEMS USING MATRICES

In Lesson 4.3 you learned how to solve a system of linear equations using Cramer’srule. Here you will learn to solve a system using inverse matrices.

In the activity you learned that a linear system can be written as a matrix equation AX = B. The matrix A is the coefficient matrix of the system, X is the and B is the

Writing a Matrix Equation

Write the system of linear equations as a matrix equation.

º3x + 4y = 5 Equation 1

2x º y = º10 Equation 2

SOLUTION

A X B

F G F G = F G. . . . . . . . . .

Once you have written a linear system as AX = B, you can solve for X by multiplyingeach side of the matrix by Aº1 on the left.

AX = B Write original matrix equation.

Aº1AX = Aº1B Multiply each side by Aº1.

IX = Aº1B Aº1A = I

X = Aº1B IX = X

5º10

xy

4º1

º32

E X A M P L E 1

matrix of constants.matrix of variables,

GOAL 1

Solve systems of

linear equations using

inverse matrices.

Use systems of

linear equations to solve

real-life problems, such as

determining how much

money to invest in Example 4.

. To solve real-lifeproblems, such as planning

a stained glass project in

Ex. 42.


GOAL 2

GOAL 1


4.5R

EAL LIFE

REA

L LIFE

Investigating Matrix Equations

Write the left side of the matrix equation as a single matrix. Then F GF G = F G Matrix equation

equate corresponding entries of the matrices. What do you obtain?

Use what you learned in Step 1 to 2x º y = º4 Equation 1

write the following linear system º4x + 9y = 1 Equation 2

as a matrix equation.

2

86

xy

º42

51

1

DevelopingConcepts

ACTIVITY

� � � � � � �

4.5 Solving Systems Using Inverse Matrices 231

SOLUTION OF A LINEAR SYSTEM Let AX = B represent a system of linearequations. If the determinant of A is nonzero, then the linear system has exactly one solution, which is X = Aº1B.

Solving a Linear System

Use matrices to solve the linear system in Example 1.

º3x + 4y = 5 Equation 1

2x º y = º10 Equation 2

SOLUTION

Begin by writing the linear system in matrix form, as in Example 1. Then find theinverse of matrix A.

Aº1 = }3 º1

8} F G = 3 4Finally, multiply the matrix of constants by Aº1.

X = Aº1B = 3 4F G = F G = F Gc The solution of the system is (º7, º4). Check this solution in the original

equations.

Using a Graphing Calculator

Use a matrix equation and a graphing calculator to solve the linear system.

2x + 3y + z = º1 Equation 1

3x + 3y + z = 1 Equation 2

2x + 4y + z = º2 Equation 3

SOLUTION

The matrix equation that represents the system is F G F G = F G.

Using a graphing calculator, you can solve the system as shown.

Enter matrix A. Enter matrix B. Multiply B by Aº1.

c The solution is (2, º1, º2). Check this solution in the original equations.

[A]-1[B]

[[2 ]

[-1]

[-2]]

MATRIX [B] 3X1

[-1 ]

[1 ]

[-2 ]

MATRIX [A] 3X3

[2 3 1 ]

[3 3 1 ]

[2 4 1 ]

º11

º2

xyz

111

334

232

E X A M P L E 3

xy

º7º4

5º10

}54

}

}

35}

}51

}

}

25}

}54

}

}

35}

}51

}

}

25}

º4º3

º1º2

E X A M P L E 2

STUDENT HELP

Study TipRemember that you canuse the method shown inExamples 2 and 3 providedA has an inverse. If Adoes not have an inverse,then the system has eitherno solution or infinitelymany solutions, and youshould use a differenttechnique.

Look Back For help with systems of linear equations, see p. 150.

STUDENT HELP

� � � � � � � USING LINEAR SYSTEMS IN REAL LIFE

Writing and Using a Linear System

INVESTING You have $10,000 to invest. You want to invest the money in a stockmutual fund, a bond mutual fund, and a money market fund. The expected

annual returns for these funds are given in the table.

You want your investment to obtain an overall annual return of 8%. A financial planner recommends that you invest the same amount in stocks as in bonds and the money market combined. How much should you invest in each fund?

SOLUTION

+ + =

0.10 + 0.07 + 0.05 = 0.08

= +

Stock amount = Money market amount =

Bond amount = Total invested = 10,000

+ + = 10,000 Equation 1

0.10 + 0.07 + 0.05 = 0.08 (10,000) Equation 2

= + Equation 3

First rewrite the equations above in standard form and then in matrix form.

s + b + m = 10,0000.10s + 0.07b + 0.05m = 800 F G F G = F Gs º b º m = 0

Enter the coefficient matrix A and the matrix of constants B into a graphingcalculator. Then find the solution X = Aº1B.

c You should invest $5000 in the stock mutual fund, $2500 in the bond mutual fund,and $2500 in the money market fund.

[A]-1[B]

[[5000]

[2500]

[2500]]

MATRIX [B] 3X1

[10000 ]

[800 ]

[0 ]

MATRIX [A] 3X3

[1 1 1 ]

[.1 .07 .05 ]

[1 -1 -1 ]

10,000800

0

sbm

10.05º1

10.07º1

10.1

1

mbs

mbs

mbs

b

ms

MMamount

Bondamount

Stockamount

Totalinvested

MMamount

Bondamount

Stockamount

Totalinvested

MMamount

Bondamount

Stockamount

E X A M P L E 4

GOAL 2


INVESTING

Each year studentsacross the country in grades4 through 12 invest ahypothetical $100,000 instocks to compete in theStock Market Game. Studentscan enter their transactionsusing the internet.

APPLICATION LINK


INT

ERNET

RE

AL LIFE

RE

AL LIFE

FOCUS ON

APPLICATIONS

ALGEBRAIC

MODEL

LABELS

VERBAL

MODEL

Investment Expected return

Stock mutual fund 10%

Bond mutual fund 7%

Money market (MM) fund 5%

¡ ¢ £ ¤ ¥ ¦ § ¨


1. What are a matrix of variables and a matrix of constants, and how are they usedto solve a system of linear equations?

2. If |A|≠ 0, what is the solution of AX = B in terms of A and B?

3. Explain why the solution of AX = B is not X = BAº1.

Write the linear system as a matrix equation.

4. x + y = 8 5. x + 3y = 9 6. x + y + z = 102x º y = 6 4x º 2y = 7 5x º y = 1

3x + 4y + z = 8

Use an inverse matrix to solve the linear system.

7. x + y = 2 8. ºx º 2y = 3 9. 4x + 3y = 67x + 8y = 21 2x + 8y = 1 6x º 2y = 10

10. INVESTING Look back at Example 4 on page 232. Suppose you have $60,000 to invest and you want an overall annual return of 9%. Use the expected annual returns shown to determine how much you should invest in each fund. Assume you are investing as much in stocks as in bonds and the money market combined.

WRITING MATRIX EQUATIONS Write the linear system as a matrix equation.

11. x + y = 5 12. x + 2y = 6 13. 5x º 3y = 93x º 4y = 8 4x º y = 5 º4x + 2y = 10

14. 2x º 5y = º11 15. x + 8y = 4 16. 2x º 5y = 4º3x + 7y = 15 4x º 5y = º11 x º 3y = 1

17. x º 4y + 5z = º4 18. 3x º y + 4z = 16 19. 0.5x + 3.1y º 0.2z = 5.92x + y º 7z = º23 2x + 4y º z = 10 1.2x º 2.5y + 0.7z = 2.2º4x + 5y + 2z = 38 x º y + 3z = 31 0.3x + 4.8y º 4.3z = 4.8

20. x + z = 9 21. 8y º 10z = º23 22. x + y º z = 0ºx º y + 2z = 6 6y º 12z = 14 2x º z = 12x + 7y º z = º4 º9x + 5z = 0 y + z = 2

SOLVING SYSTEMS Use an inverse matrix to solve the linear system.

23. 3x + y = 8 24. x + y = º1 25. 2x + 7y = º535x + 2y = 11 11x + 12y = 8 x + 3y = º22

26. 7x + 5y = 8 27. 5x º 7y = 54 28. º5x º 7y = º94x + 3y = 4 2x º 4y = 30 2x + 3y = 3

29. x + 2y = º9 30. 2x + 4y = º26 31. 9x º 5y = 43º2x º 3y = 14 2x + 5y = º31 º2x + 2y = º22


GUIDED PRACTICE


Concept Check ✓

Skill Check ✓

Investment Expected return

Stock mutual fund 12%

Bond mutual fund 8%

Money market fund 5%


STUDENT HELP

STUDENT HELP

HOMEWORK HELP

Example 1: Exs. 11–22Example 2: Exs. 23–31Example 3: Exs. 32–39Example 4: Exs. 40–44

¡ ¢ £ ¤ ¥ ¦ § ¨


SOLVING SYSTEMS Use the given inverse of the coefficient matrix to solve

the linear system.

32. 2y º z = º2 33. x º y º 3z = 95x + 2y + 3z = 4 5x + 2y + z = º307x + 3y + 4z = º5 º3x º y = 4

Aº1 = F G Aº1 = F GSOLVING SYSTEMS Use an inverse matrix and a graphing calculator to

solve the linear system.

34. 3x + 2y = 13 35. ºx + y º 3z = º4 36. 3x + 5y º 5z = 213x + 2y + z = 13 3x º 2y + 8z = 14 º4x + 8y º 5z = 12x + y + 3z = 9 2x º 2y + 5z = 7 2x º 5y + 6z = º16

37. 2x + z = 2 38. 4x + 3y + z = 14 39. x + y º 3z = º175x º y + z = 5 6x + y = 9 2x + z = 12ºx + 2y + 2z = 0 3x + 5y + 3z = 21 º7x º 2y + z = º11

40. SKATING PARTY You are planning a birthday party for your youngerbrother at a skating rink. The cost of admission is $3.50 per adult and $2.25 perchild, and there is a limit of 20 people. You have $50 to spend. Use an inversematrix to determine how many adults and how many children you can invite.

41. DENTAL FILLINGS Dentists use various amalgams for silver fillings. Thematrix shows the percents (expressed as decimals) of powdered alloys used inpreparing three different amalgams. Suppose a dentist has 5483 grams of silver,2009 grams of tin, and 129 grams of copper. How much of each amalgam can be made?

PERCENT ALLOY BY WEIGHT

Amalgam

A B C

F G42. STAINED GLASS You are making mosaic tiles from three types of stained

glass. You need 6 square feet of glass for the project and you want there to be asmuch iridescent glass as red and blue glass combined. The cost of a sheet ofglass having an area of 0.75 square foot is $6.50 for iridescent, $4.50 for red, and$5.50 for blue. How many sheets of each type should you purchase if you plan tospend $45 on the project?

43. WALKWAY LIGHTING A walkway lighting package includes a transformer,a certain length of wire, and a certain number of lights on the wire. The price ofeach lighting package depends on the length of wire and the number of lights onthe wire.

• A package that contains a transformer, 25 feet of wire, and 5 lights costs $20.• A package that contains a transformer, 50 feet of wire, and 15 lights costs $35.• A package that contains a transformer, 100 feet of wire, and 20 lights costs $50.

Write and solve a system of equations to find the cost of a transformer, the costper foot of wire, and the cost of a light. Assume the cost of each item is the samein each lighting package.

0.730.270.00

0.720.250.03

0.700.260.04

Silver

Tin

Copper

5º16

7

3º9

4

1º3

1

8º5

º10

º117

14

º111

DENTIST

Dentists diagnose,prevent, and treat problemsof the teeth and mouth.Dental amalgams have beenused for more than 150 yearsto restore the teeth of over100 million Americans.

CAREER LINK


INT

ERNET

RE

AL LIFE

RE

AL LIFE

FOCUS ON

CAREERS

HOMEWORK HELP

Visit our Web sitewww.mcdougallittell.comfor help with Exs. 32 and 33.

INT

ERNET

STUDENT HELP

¡ ¢ £ ¤ ¥ ¦ § ¨


44. CONSTRUCTION BUSINESS You are an accountant for a constructionbusiness and are planning next year’s budget. You have $200,000 to spend onsalaries, equipment maintenance, and other general expenses. Based on previousfinancial records of the business, you expect to spend five times as much onsalaries as on equipment maintenance, and you expect general expenses to be10% of the amount spent on the other two categories combined. Write and solvea system of equations to find the amount you should budget for each category.

45. MULTI-STEP PROBLEM A company sells different sizes of gift baskets witha varying assortment of meat and cheese. A basic basket with 2 cheeses and 3 meats costs $15, a big basket with 3 cheeses and 5 meats costs $24, and asuper basket with 7 cheeses and 10 meats costs $50.

a. Write and solve a system of equations using the information about the basicand big baskets.

b. Write and solve a system of equations using the information about the big andsuper baskets.

c. Writing Compare the results from parts (a) and (b) and make a conjectureabout why there is a discrepancy.

46. SOLVING SYSTEMS OF FOUR EQUATIONS Solve the linear system using thegiven inverse of the coefficient matrix.

w + 6x + 3y º 3z = 22w + 7x + y + 2z = 5w + 5x + 3y º 3z = 3º6x º 2y + 3z = 6

EVALUATING FUNCTIONS Evaluate ƒ(x) or g(x) for the given value of x.

(Review 2.7)

ƒ(x) = g(x) =

47. ƒ(8) 48. ƒ(11) 49. ƒ(º2) 50. ƒ(0)

51. g(3) 52. g(0) 53. g(º1) 54. g(º3)

GRAPHING FUNCTIONS Graph the function and label the vertex.

(Review 2.8 for 5.1)

55. y = |x º 5| 56. y = |x| + 8 57. y = º|x º 8| º 9

58. y = |x º 5| + 4 59. y = º|x + 3| + 4 60. y = º|x + 6| º 2

FINDING INVERSES Find the inverse of the matrix. (Review 4.4)

61. F G 62. F G 63. F G64. F G 65. F G 66. F Gº2

º267

42

73

º5º1

113

17º2

8º1

21

52

º43

7º5

}

18}x + 8, if x < º1

2x º 1, if x ≥ º1

}

34}x º 8, if x ≤ 8

ºx + 6, if x > 8

MIXED REVIEW

TestPreparation

★★Challenge

Aº1 = 3 490

º8º5

º33º13320

º3032

401

º39º24

EXTRA CHALLENGE


¡ ¢ £ ¤ ¥ ¦ § ¨


Find the inverse of the matrix. (Lesson 4.4)

1. F G 2. F G 3. F G 4. F GUse an inverse matrix to solve the linear system. (Lesson 4.5)

5. 4x + 7y = 24 6. º9x + 13y = 3 7. 8x + 7y = 3x + 2y = 7 2x º 3y = º1 º2x º 2y = 0

8. BUYING FLATWARE The price of flatware varies depending on the numberof place settings you buy as well as other items included in the set. Suppose a setwith 4 place settings costs $142 and a set with 8 place settings and a serving setcosts $351. Find the cost of a place setting and a serving set. Assume that thecost of each item is the same for each flatware set. (Lesson 4.5)

57

68

1º3

º69

5º3

º74

12

47

QUIZ 2 Self-Test for Lessons 4.4 and 4.5

Systems of Equations

THENTHENOVER 2000 YEARS AGO, a method for solving systems of equations using rectangulararrays of counting rods was presented in Nine Chapters on the Mathematical Art, anearly Chinese mathematics text. A problem from this book is given below.

Three bundles of top-grade ears of rice, two bundles of medium-grade ears ofrice, and one bundle of low-grade ears of rice make 39 dou (of rice by volume);two bundles of top-grade ears of rice, three bundles of medium-grade ears ofrice, and one bundle of low-grade ears of rice make 34 dou; one bundle of top-grade ears of rice, two bundles of medium-grade ears of rice, and three bundlesof low-grade ears of rice make 26 dou. How many dou are there in a bundle ofeach grade of rice?

Top-grade ears of rice

Medium-grade ears of rice

Low-grade ears of rice

Total produce

1. Use matrices to organize the given information and solve the problem.

2. How is the arrangement of counting rods similar to your matrices? How is it different?

TODAY, computers use matrices representing systems with many variables to solve complicated problems like predicting weather and designing aircraft.NOWNOW

Great Wall of

China planned

Chinese method of

solving systems described

Mechanical

calculator,

France1642

c. 220 B .C .

Electronic

computers, USA

c. 1940A .D . 50

APPLICATION LINK


INT

ERNET

© ª « ¬ ® ¯ °

Chapter 4 Extension 237

Solving Systems UsingAugmented Matrices

USING ELEMENTARY ROW OPERATIONS

A matrix containing the coefficient matrix and the matrix of constants for a system oflinear equations is called the of the system.

LINEAR SYSTEM AUGMENTED MATRIX

F GRecall from Chapter 3 that equations in a system can be multiplied by a constant, or amultiple of one equation can be added to another equation. Similar operations can beperformed on the rows of an augmented matrix to solve the corresponding system.

To solve a system, use elementary row operations to transform the originalaugmented matrix into a matrix having 1’s along the main diagonal and 0’s below the main diagonal. A matrix of this form is said to be in triangular form.

Using Row Operations to Solve a Two-Variable System

LINEAR SYSTEM

x º 2y = 7º3x + 5y = º4

Add 3 times the first equation to the second equation. You get this system:

x º 2y = 7ºy = 17

Multiply the second equation by º1.

x º 2y = 7y = º17

The second row of the matrix tells you that y = º17. Substitute º17 for y in theequation for the first row: x º 2(º17) = 7, or x = º27. The solution is (º27, º17).

E X A M P L E 1

7º4

::

º25

1º3

x º 2y = 7º3x + 5y = º4

augmented matrix

GOAL

Solve systems of

linear equations using

elementary row operations

on augmented matrices.

The use of augmented

matrices allows you to solve

a linear system by

suppressing the variables

and working only with the

coefficients and constants.


GOAL


Extension

Two augmented matrices are row-equivalent if their corresponding systems

have the same solution(s). Any of these row operations performed on an

augmented matrix will produce a matrix that is row-equivalent to the original:

• Interchange two rows.

• Multiply a row by a nonzero constant.

• Add a multiple of one row to another row.

ELEMENTARY ROW OPERATIONS

.

AUGMENTED MATRIX

F GAdd 3 times the first row, R1, to thesecond row, R2.

3R1 + R2 ˘ F GMultiply the second row by º1.

(º1)R2 ˘ F G7º17

::

º21

10

717

::

º2º1

10

7º4

::

º25

1º3

C H A P T E R 4

.

.

.

± ² ³ ´ µ ¶ · ¸


Using Row Operations to Solve a Three-Variable System

LINEAR SYSTEM

2x + 4y + 5z = 5x + 3y + 3z = 2

2x + 4y + 6z = 2

Add º1 times the first equation to the third equation. You get this system:

2x + 4y + 5z = 5x + 3y + 3z = 2

z = º3

Add º0.5 times the first equation to the second equation.

2x + 4y + 5z = 5y + 0.5z = º0.5

z = º3

Multiply the first equation by 0.5.

x + 2y + 2.5z = 2.5y + 0.5z = º0.5

z = º3

The third row of the matrix tells you that z = º3. Substitute º3 for z in the equationfor the second row, y + 0.5z = º0.5, to obtain y + 0.5(º3) = º0.5, or y = 1. Thensubstitute º3 for z and 1 for y in the equation for the first row, x + 2y + 2.5z = 2.5,to obtain x + 2(1) + 2.5(º3) = 2.5, or x = 8. The solution is (8, 1, º3).

EXERCISES

SOLVING SYSTEMS Use an augmented matrix to solve the linear system.

1. 6x + 4y = 8 2. x + y = 2 3. x + 2y = º93x + 3y = 9 7x + 8y = 21 º2x º 3y = 14

4. x º 3y = 5 5. 3x + 2y = 2 6. x + y = º1º2x º 4y = 20 5x º 6y = 50 7x + 9y = º19

7. º2x º y = º5 8. 9x º 4y = 2 9. º12x + 15y = 36x + 5y = 17 º6x º 16y = º6 º7x º 20y = º4

10. 2x + 6y + 3z = 2 11. 2x + 6y + 3z = 8 12. 2x + 10y = 28x + 3y + z = 1 x + 5y + 5z = 1 x + 3y + 4z = 22x + 5y + 2z = º1 x + 3y + z = 3 x + 5y º z = 10

13. x + 4y º 2z = 3 14. x º y + 3z = 6 15. x + 2z = 4x + 3y + 7z = 1 x º 2y = 5 x + y + z = 62x + 9y + z = 8 2x º 2y + 5z = 9 3x + 3y + 4z = 28

16. CRITICAL THINKING Try using an augmented matrix to solve the given system.What happens? What can you say about the system’s solution(s)?

x º 2y + 7z = 65x º 10y + 35z = 303x º 6y + 21z = 18

E X A M P L E 2

AUGMENTED MATRIX

F GAdd º1 times the first row to the third row.

(º1)R1 + R3 ˘F G

Add º0.5 times the first row to the second row.

º0.5R1 + R2 ˘ F GMultiply the first row by 0.5.

0.5R1 ˘ F G2.5º0.5

º3

:::

2.50.5

1

210

100

5º0.5

º3

:::

50.5

1

410

200

52

º3

:::

531

430

210

522

:::

536

434

212

.

.

.

.

.

.

.

.

± ² ³ ´ µ ¶ · ¸Chapter SummaryCHAPTER

4

WHAT did you learn?

Use matrices and determinants in real-life situations. (4.1–4.5)

Perform matrix operations.• add and subtract matrices (4.1)

• multiply a matrix by a scalar (4.1)

• multiply two matrices (4.2)

Evaluate the determinant of a matrix. (4.3)

Find the inverse of a matrix. (4.4)

Solve matrix equations. (4.1, 4.4, 4.5)

Solve systems of linear equations.• using Cramer’s rule (4.3)

• using inverse matrices (4.5)

Use systems of linear equations to solve real-lifeproblems. (4.3, 4.5)

How does Chapter 4 fit into the BIGGER PICTURE of algebra?

Your study of linear algebra has continued with Chapter 4. Matrices are usedthroughout linear algebra, especially for solving linear systems. This introductionto matrices, their uses, and properties of matrix operations also connects to yourpast. For example, instead of multiplying real numbers, or variables that representreal numbers, you multiplied matrices. You also saw properties, such as thecommutative property of multiplication, that apply to real numbers but notto matrices.

Did you write out the steps?

Here is an example of severalsteps you can write whenmultiplying two matrices,following the Study Strategy

on page 198.

STUDY STRATEGY

239

Writing Out the Steps

F GF G= F G= F G= F Gº42

14

323

0 º 420 + 14

º9 + 1227 º 4

1(0) + (º6)7º3(0) + 2(7)

1(º9) + (º6)(º2)º3(º9) + 2(º2)

07

º9º2

º62

1º3

WHY did you learn it?

Organize data, such as the number and dollar value ofHispanic music products shipped. (p. 204)

Find the total cost of college tuition plus room andboard. (p. 205)

Write U.S. population data as percents of totalpopulation. (p. 205)

Calculate the cost of softball equipment. (p. 210)

Find the area of the Golden Triangle. (p. 220)

Encode or decode a cryptogram. (pp. 225, 226)

Extend the process of equation solving to equationswhose solutions are matrices. (pp. 201, 224)

Find the cost of gasoline. (p. 220)

Calculate a budget. (p. 235)

Decide how much money to invest in each of threetypes of mutual funds. (p. 232)

± ² ³ ´ µ ¶ · ¸


Chapter ReviewCHAPTER

4

• matrix, p. 199

• dimensions of a matrix, p. 199

• entries of a matrix, p. 199

• row matrix, p. 199

• column matrix, p. 199

• square matrix, p. 199

• zero matrix, p. 199

• equal matrices, p. 199

• scalar, p. 200

• determinant, p. 214

• Cramer’s rule, p. 216

• coefficient matrix, p. 216

• identity matrix, p. 223

• inverse matrix, p. 223

• matrix of variables, p. 230

• matrix of constants, p. 230

VOCABULARY

4.1 MATRIX OPERATIONS

You can add or subtract matrices that have the same dimensions byadding or subtracting corresponding entries.

F G + F G = F G = F GYou cannot subtract these matrices because they have different dimensions.

F G º F GTo do scalar multiplication, multiply each entry in the matrix by the scalar.

º3F G = F G = F GTo solve this matrix equation, equate corresponding entries and solve for x and y.

F G = F G23y

º6º1

29

x + 2º1

18º3

º24

36º9º6

(º3)(º6)(º3)(1)(º3)(8)

(º3)(º12)(º3)(3)(º3)(2)

º618

º1232

º41

º57

12

1º3

º20

º110

14º4

º2 + 16 + 4

5 + 90 + (º4)

14

9º4

º26

50

Examples onpp. 199–202

Perform the indicated operation if possible. If not possible, state the reason.

1. F G º F G 2. F G º F G 3. F G + F G4. F G +F G 5. 2F G 6. }

12}F G

Solve the matrix equation for x and y.

7. F G = F G 8. F G + F G = F G9. F G + F G = F G 10. F G º F G = F Gº7

86

º25

º31x

º25

7y

º311

º323

º4º2

0x

3y

º124

º713

º3x

50

º68

4y

133

º11410

y º 95

1410

1º5x

08

º2

º24

º6

º121

6º511

4100

º21

º3

142

51

º4

132

0º2

1

177

204

106

º1

694

5º3

º21

3º4

97

02

412

153

EXAMPLES

x + 2 = º6 3y = 9x = º8 y = 3

± ² ³ ´ µ ¶ · ¸

Chapter Review 241

4.2 MULTIPLYING MATRICES

You can multiply a matrix with n columns by a matrix with n rows.

F GF G = F G = F Gº1713

º3630

(º6)(3) + (1)(1)(5)(3) + (º2)(1)

(º6)(6) + (1)(0)(5)(6) + (º2)(0)

31

60

1º2

º65


Write the product. If it is not defined, state the reason.

11. F Gf g 12. F GF G 13. F GF G88

º1º4

32

79

10

120

º51

1510

2º3

º7º1012

º4

4.3 DETERMINANTS AND CRAMER’S RULE

You can evaluate the determinant of a 2 ª 2 or a 3 ª 3 matrix. Find products of the entries on the diagonals and subtract.

det F G = * * = º2(4) º 1(º6) = º8 + 6 = º2

det F G = * * = (24 + 6 + 20) º [60 + (º24) + (º2)] = 16

You can find the area of a triangle with vertices (x1, y1), (x2, y2), and (x3, y3) using

Area = 6 }21

} * *where 6 indicates you should choose the sign that yields a positive value.

You can use Cramer’s rule to solve a system of linear equations. First find thedeterminant of the coefficient matrix and then use Cramer’s rule to solve for x and y.

3x º 4y = 12x + 2y = 14

det F G = * * = 3(2) º 1(º4) = 6 + 4 = 10

x = }10} = = }81

00} = 8 y = }10} = }

3(14)1º0

1(12)} = }

31

00} = 3

12(2) º 14(º4)}}10

º42

31

º42

31

111

y1y2y3

x1x2x3

16

º4

2º1

2

532

16

º4

2º1

2

532

16

º4

2º1

2

º64

º21

º64

º21



14. F G 15. F G 16. F G 17. F G18. Find the area of a triangle with vertices A(0, 1), B(2, 4), and C(1, 8).

Use Cramer’s rule to solve the linear system.

19. 7x º 4y = º3 20. 2x + y = º2 21. 5x º 4y + 4z = 182x + 5y = º7 x º 2y = 19 ºx + 3y º 2z = 0

4x º 2y + 7z = 3

4º2º3

º312

201

014

113

320

º31

62

12

º93

EXAMPLE

EXAMPLES

* *1214

31* *º4

21214

¹ º » ¼ ½ ¾ ¿ À


IDENTITY AND INVERSE MATRICESExamples onpp. 222–226

Find the inverse of the matrix.

22. F G 23. F G 24. F G 25. F GSolve the matrix equation.

26. F GX = F G 27. F GX + F G = F Gº32

96

º21

86

º53

º74

94

0º1

32

53

º11

6º5

6º4

º32

23

21

311

27

4.5

4.4

SOLVING SYSTEMS USING INVERSE MATRICES

You can use inverse matrices to solve a system of linear equations.

x + 3y = 10 F G F G = F G2x + 5y = º2

A X = B

Then X = Aº1B = }1(5) º

12(3)

} F G F G = º1F G = F G.

The solution is (º56, 22).

º5622

56º22

10º2

º31

5º2

10º2

x

y

35

12


Use an inverse matrix to solve the linear system.

28. 9x + 8y = º6 29. x º 3y = º2 30. 4x º 14y = º15ºx º y = 1 5x + 3y = 17 18x º 12y = 9

Use an inverse matrix and a graphing calculator to solve the linear system.

31. x º y º 4z = 3 32. 4x + 10y º z = º3 33. 5x º 3y + 5z = º1ºx + 3y º z = º1 11x + 28y º 4z = 1 3x + 2y + 4z = 11x º y + 5z = 3 º6x º 15y + 2z = º1 2x º y + 3z = 4

You can find the inverse of an n ª n matrix provided its determinantdoes not equal zero.

The inverse of A = F G is Aº1 = F G.

If A = F G, then Aº1 = }7(2) º

15(3)

} F G = º1F G = F G.

You can use the inverse of a matrix A to solve a matrix equation AX = B: X = Aº1B.

F GX = F GAº1 = }7 º

16} F G = F G

X = F GF G = F Gº62

6º1

02

35

º31

7º2

º31

7º2

º31

7º2

02

35

37

12

3º7

º25

º37

2º5

º37

2º5

32

75

ºb

a

d

ºc

1}

|A|b

d

a

c

EXAMPLES

EXAMPLE

Write in matrix form.

¹ º » ¼ ½ ¾ ¿ À

Chapter Test 243

Chapter TestCHAPTER

4

ÁÁ(1, 7)

(2, 2)

(4, 5) ÂÃ

Perform the indicated operation(s).

1. F G + F G 2. 0.25F G 3. º4SF G º F GD4. F GF G 5. F G F G 6. F GF G

Solve the matrix equation for x and y.

7. F G = F G 8. F G = F G 9. 3F G = F GEvaluate the determinant of the matrix.

10. F G 11. F G 12. F G 13. F GFind the area of the triangle with the given vertices.

14. A(2, 1), B(5, 3), C(7, 1) 15. A(º1, 0), B(º3, 3), C(0, 4) 16. A(º3, 2), B(º1, 4), C(º4, 3)

Use Cramer’s rule to solve the linear system.

17. 2x + y = 12 18. º4x + 5y = º10 19. x + y = 2 20. 5x º 2y + 7z = 125x + 3y = 27 5x º 6y = 13 2y º z = 0 2x + 5y + 3z = 10

ºx º y + z = º1 3x º y + 4z = 8Find the inverse of the matrix.

21. F G 22. F G 23. F G 24. F GSolve the matrix equation.

25. F GX = F G 26. F GX = F G 27. F GX = F GUse an inverse matrix to solve the linear system.

28. x º y = 5 29. 3x + 2y = º8 30. 2x º 7y = 6º2x + 3y = º9 º2x + 5y = 18 º3x + 11y = º10

31. STAINED GLASS You are making a stained glass panel using different colors asshown. The coordinates given are measured in inches. Find the area of the red triangle.

32. DECODING Use the inverse of A = F G and the coding information on

pages 225 and 226 to decode the message below.

44, º15, 3, º1, 80, º32, 39, º17, 3, º1, 12, º4, 77, º26

33. BUDGETING MEALS You have $18 to spend for lunch during a 5 day workweek. It costs you about $1.50 to make a lunch at home and about $5 to buy alunch. How many times each work week should you make a lunch at home?

º1º1

23

82

612

104

02

1º6

01

10

56

22

º69

3º2

71

81

0º5

10

4º5

º66

º21

º11

59

43

4º2

1

30

º5

º160

130

052

412

º1º1

º21

º94

7º3

3º12

º15y

1º4

x

894

2x

19

ºy

º221

83

º1º9

y + 63

º1x º 4

001

260

º141

01

º1

1º1

2

020

04

3º5

12

º69

º226

4º3

0

183

4º1

4

8º8

4º3

10º6

1º4

º1236

20º4

8º8

77

2º5

3º2

º4º2

50

23

Ä Å Æ Ç È É Ê Ë


Chapter Standardized TestCHAPTER

4

1. MULTIPLE CHOICE Which matrix equals

2SF G + F GD?

¡A F G ¡B F G¡C F G ¡D F G¡E F G

2. MULTIPLE CHOICE What are the values of x and yin the matrix equation?

2xF G = F G¡A x = 8, y = º80 ¡B x = º4, y = º80

¡C x = 4, y = 80 ¡D x = 4, y = º80

¡E x = 2, y = º40

3. MULTIPLE CHOICE What is the product of

F G and F G?


4. MULTIPLE CHOICE What is the determinant of

F G?

¡A º78 ¡B º34 ¡C º16

¡D 34 ¡E 78

5. MULTIPLE CHOICE What is the inverse of

F G?


6. MULTIPLE CHOICE Which matrix has no inverse?


7. MULTIPLE CHOICE What is the area of the trianglein square units?

¡A 40 ¡B 30 ¡C 26

¡D 20 ¡E 13

8. MULTIPLE CHOICE What is the solution of thelinear system?

7x + 5y = 64x + 3y = 3

¡A x = 3, y = 3 ¡B x = º3, y = º3

¡C x = 3, y = º3 ¡D x = º3, y = 3

¡E x = 8, y = º10

(23, 4)

(2, 21)

(6, 3)ÌÃÍÎ

41

º42

11

10

46

º23

6º9

4º6

05

60

59

º4º7

º5º9

47

º5º9

º4º7

59

º47

º5º9

4º7

º5º4

97

52

º2

1º1

4

2º3

0

º28

º3

2113

º2

º22

º3

19132

º22

º7

1913

º2

º2º6º3

1913

º2

º22

º3

1913

º2

º21

º1

105

43

º1

012

º1º2

3

º840

º16y

º15

º2º10

º10476

42º18

6030

º24º6

º2220

6º12

º2418

4º14

º418

4º2

º56

0º3

º73

2º4

TEST-TAKING STRATEGY During a test it is important to stay mentally focused, but also

physically relaxed. If you start to get tense, put your pencil down and take some deep breaths.

This may help you regain control.

Ä Å Æ Ç È É Ê Ë

Chapter Standardized Test 245

9. QUANTITATIVE COMPARISON Choose the statement that is true about thegiven quantities.

¡A The quantity in column A is greater.

¡B The quantity in column B is greater.

¡C The two quantities are equal.

¡D The relationship cannot be determined from the given information.

10. MULTI-STEP PROBLEM The School Spirit club ordered shirts to sell atbasketball games. The number of each size and type of shirt they ordered is shown in the matrix at the right.

a. At the first basketball game the club sold 17 T-shirts (4 small, 5 medium, 6 large, and 2 extra large) and 12 sweatshirts (3 medium, 5 large, and 4 extralarge). Write a matrix that gives the number of each size and type of shirt sold at the game. Then write a matrix that shows the number of shirts left.

b. The wholesale price of a T-shirt is $8, and the club sells them for $10 each.The wholesale price of a sweatshirt is $20, and the club sells them for $25each. Write a row matrix for the number of each type of shirt (T-shirt orsweatshirt) sold at the game from part (a). Write a column matrix for the profit on each type of shirt. Multiply the row matrix by the column matrix and interpret the result.

11. MULTI-STEP PROBLEM You and a friend are planning a secret meeting.

You agree that A = F G will be your coding matrix. Use the coding

information on pages 225 and 226.

a. Use matrix A to encode the message SATURDAY.

b. Use the inverse of A to decode your answer to part (a).

c. Your friend replied with the message below. Use the inverse of A to decode it.

34, 49, 6, 9, 23, 41, 6, 12, 14, 19, 16, 20

d. Use matrix A to encode your answer to part (c).

12. MULTI-STEP PROBLEM Use the following linear system.

x º 2y = 13x º 5y = 4

a. Use Cramer’s rule to solve the system.

b. Use inverse matrices to solve the system.

c. Use the substitution or linear combination method to solve the system.

d. Solve the system by graphing. Label the solution on your graph.

e. Writing Which method do you prefer for solving this linear system?

12

11

Column A Column B

det F G det F Gº15

º23

12

0º8

FUNDRAISING

T-shirt Sweatshirt

3 420204020

2525

10050

S

M

L

XL

MATRICES AND DETERMINANTS - Mr. Odoom's Math...

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