Page 133 - Basic College Mathematics with Early Integers

110 C HAPTE R 2 I INTEGERS AND INTRODUCTION TO VARIABLES

If x is 7, then 3x becomes
Î
#
3x = 3 7
= 21
Replacing a variable in an expression by a number and then finding the value
of the expression is called evaluating the expression for the variable. When finding
the value of an expression, remember to follow the order of operations given in
Section 1.9.

PRACTICE 1 Example 1 Evaluate x + 7 if x is 8.
Evaluate x - 2 if x is 5.
Solution: Replace x with 8 in the expression x + 7.

Î
x + 7 = 8 + 7 Replace x with 8.
= 15 Add.
Work Practice 1

When we write a statement such as “x is 5,” we can use an equal symbol to
represent “is” so that
x is 5 can be written as x = 5.

PRACTICE 2 Example 2 Evaluate 21x - y2 for x = 8 and y = 4.
Evaluate y1x - 32 for x = 3
and y = 7. Solution: 21x - y2 = 218 - 42 Replace x with 8 and y with 4.
= 2142 Subtract.
= 8 Multiply.
Work Practice 2

x - 5y
PRACTICE 3 Example 3 Evaluate for x = 21 and y = 3.
y
y + 6
Evaluate for x = 2 and x - 5y
x Solution: 21 - 5132
y = 8. y = 3 Replace x with 21 and y with 3.
21 - 15
= Multiply.
3
6
= Subtract.
3
= 2 Divide.
Work Practice 3

PRACTICE 4 Example 4 Evaluate x + z - 3 for x = 5 and z = 4.
2
Evaluate 25 - z + x for z = 2
3
2
2
and x = 1. Solution: x + z - 3 = 5 + 4 - 3 Replace x with 5 and z with 4.
2
= 25 + 4 - 3 Evaluate 5 .
= 26 Add and subtract from left to right.
Work Practice 4 Copyright 2012 Pearson Education, Inc.

Answers
1. 3 2. 0 3. 7 4. 18