Ch 2 Sec 3: Slide #1

Columbus State Community College

Chapter 2 Section 3

Solving Equations Using Addition

Ch 2 Sec 3: Slide #2

Solving Equations Using Addition

1. Determine whether a given number is a solution of an equation.

2. Solve equations, using the addition property of equality.

3. Simplify equations before using the addition property of equality.

Ch 2 Sec 3: Slide #3

Note on Identifying Equations

NOTE

An equation has an equal sign. Notice the similarity in the words equation and equal. An expression does not have an equal sign.

Ch 2 Sec 3: Slide #5

The Solution of an Equation

NOTE

Most of the equations that you will solve in this book have only one solution, that is, one number that makes the equation balance. There are some equations that have two or more solutions. We will examine such equations later in this course.

Ch 2 Sec 3: Slide #6

Identifying the Solution of an Equation

EXAMPLE 1 Identifying the Solution of an Equation

Which of these numbers, 65, 85, or 75, is the solution of the equation m – 45 = 30?

65 – 45 ≠ 3085 – 45 ≠ 3075 – 45 = 30

Replace m with each of the numbers. The one that makes the equation balance is the solution.

Does not balance:

65 – 45 is 20 and

20 is less than 30.

Does not balance:

85 – 45 is 40 and

40 is more than 30.

Balances:

75 – 45 is 30.

The solution is 75 because, when m is 75, the equation balances.

Ch 2 Sec 3: Slide #7

Addition Property of Equality

Addition Property of Equality

If a = b, then a + c = b + c and a – c = b – c.

In other words, you may add the same number to both sides of an equation and you may also subtract the same number from both sides of an equation and still keep it balanced.

Ch 2 Sec 3: Slide #9

Goal in Solving an Equation

Goal in Solving an Equation

The goal is to end up with the variable (letter) on one side of the equal sign balancing a number on the other side.

We work on the original equation until we get:

variable = number number = variableor

Once we have arrived at that point, the number balancing the variable is the solution to the original equation.

Ch 2 Sec 3: Slide #10

Using the Addition Property of Equality

EXAMPLE 2 Using the Addition Property of Equality

(a) n + 7 = 32

Solve each equation and check the solution.

n + 7 = 32

– 7 – 7

n + 7 = 25

n + 7 = 32

= 32

32

25 + 7

= 32

Check the solution:

Balance statement

Solution

Ch 2 Sec 3: Slide #11

Using the Addition Property of Equality

EXAMPLE 2 Using the Addition Property of Equality

(b) x – 3 = –15

Solve each equation and check the solution.

x – 3 = –15

+ 3 + 3

x + 7 = –12

x – 3 = –15

= –15

–15

–12 – 3

= –15

Check the solution:

Balance statement

Solution

Ch 2 Sec 3: Slide #12

CAUTION

CAUTION

When checking the solution to Example 2(b), we end up with –15 = –15. Notice that –15 is not the solution. The solution is –12, the number used to replace x in the original equation.

Balance statement

Solution

x – 3 = –15

+ 3 + 3

x + 7 = –12

x – 3 = –15

= –15

–15

–12 – 3

= –15

Ch 2 Sec 3: Slide #13

Simplifying before Solving Equations

EXAMPLE 3 Simplifying before Solving Equations

(a) c – 4 = 9 – 5

Solve each equation and check the solution.

c – 4 = 9 – 5

+ 4 + 4

c + 7 = 8

c – 4 = 9 – 5

= 4

4

8 – 4

= 4

Check:

Balance statement

Solution

c – 4 = 4

Ch 2 Sec 3: Slide #14

Simplifying before Solving Equations

EXAMPLE 3 Simplifying before Solving Equations

(b) 2v + 1 – v = 3 – 2

Solve each equation and check the solution.

2v + 1 – v = 3 – 2

– 1 – 1

v + 7 = 0

2v + 1 – v = 3 – 2

= 1

1

2 ( 0 ) + 1 – 0

= 1

Check:

Balance statement

Solution

v + 1 = 1

Ch 2 Sec 3: Slide #15

Note on Eliminating Terms

Note on Eliminating Terms

To eliminate a term from one side of an equation, we perform the opposite operation that precedes the term we want to eliminate.

Let’s take a another look at Example 2.

n + 7 = 32

– 7 – 7

n = 25

Example 2 (a)

To get the variable, n, by itself we need to eliminate the constant term, 7, from the left side of the equation. The opposite of “+ 7” is “– 7”, so we subtract 7 from both sides of the equation.

Ch 2 Sec 3: Slide #16

To get the variable, x, by itself we need to eliminate the constant term, 3, from the left side of the equation. The opposite of “– 3” is “+ 3”, so we add 3 from both sides of the equation.

x – 3 = –15

+ 3 + 3

x = –12

Example 2 (b)

Note on Eliminating Terms

Note on Eliminating Terms

To eliminate a term from one side of an equation, we perform the opposite operation that precedes the term we want to eliminate.

Let’s take a another look at Example 2.

Ch 2 Sec 3: Slide #17

Note on Eliminating Terms

Note on Eliminating Terms

To eliminate a term from one side of an equation, we perform the opposite operation that precedes the term we want to eliminate.

Let’s take a another look at Example 2.

n + 7 = 32

– 7 – 7

n = 25

Example 2 (a)

x – 3 = –15

+ 3 + 3

x = –12

Example 2 (b)

Ch 2 Sec 3: Slide #18

Solving Equations Using Addition

Chapter 2 Section 3 – Completed

Written by John T. Wallace