Today we are going to:

• write algebraic expressions by representing unknown quantities; and

• evaluate algebraic expressions by substituting the given value for the variable.

Write an algebraic expression for each of the following statements.

(a)Add 3 to p

(b) Subtract 2 from the product of 3 and x

(c) Divide the sum of

m and n by 5

(d) Multiply 7 to half of t

p + 3

3x – 2

m + n

5

7t

2

Algebraic Expression in Two or more unknown

Example :State the number of unknown in each of the following algebraic expressions.(a) 2a + 2b (b) 100 – 2pqr (c) hjk + 8p – 19q

Answer :• 2a + 2b has two unknown : a and b• 100 – 2pqr has three unknown : p, q and r• hjk + 8p – 19q has five unknown : h, j, k, p and q

Evaluating Algebraic Expression

*To evaluate an algebraic expression is to find the value of the expression.

STEPS:

1. Substitute the given value for the variables (replace letters with the given numbers)

2. Solve using the order of operations (PEMDAS)

Example :

Evaluate 2x + 5y when x = 4 and y = 2

Solution : 2x + 5y = 2 (4) + 5 (2) = 8 + 10 = 18

Evaluate p+2q+ 3r given p = 2 q = 4, r = 6

=2+ 2(4) + 3(6)

=2 + 8 + 18

=28

Example :Evaluate 3c + 5 if c = 5 and d = 1 4dSolution : 3c + 5 = 3 (5) + 5 4 d 4 (1) = 15 + 5 4 = 20 4 = 5

ALGEBRAIC EXPRESSIONS

Step 1 Substitute the given values for the variables.

Step 2 Solve using the order of Operations PEMDAS.

Problem 1

Given the formula P=2L+2W, find the value of P if K=7 and W=3.

Problem 2

If V=lwh, what is the value of V when l=2, w=3, and h=4?

Problem 3

If x=1 and y= -2, which expression has a value of 3?(a) x+y (c) x-y(b) xy (d) y-x

Problem 4

If a=1 and b=-2, find the value of (a+b)2.

Problem 5

Using the formula V=x 2h, find V when x=6 and h=2

Problem 6

Evaluate the expression (6a)2b if a=2 and b=-1

Problem 7

Find the value of 3a-4b if a=-2 and b=5.

Problem 8

Find the value of (x2-8x+4) if x=1/2.

Problem 9

Evaluate 5a2-b if a=-2 and b=10.

Problem 10

Find the value of the expression 3x3 when x=-2

Problem 11

What is the value of R2S if R=5 and S=-2.

Problem 12

Evaluate the expression 3x2 +y if x=1 and y=-3.

Problem 13

Find the value of the expression 2xy3 if x=3 and y=-2

Problem 14

Find the value of 5x2 if x=-3.

Problem 15

If x=-3 and y=2, find the value of (xy)2.