1-6 Writing Expressions

Objective (things to learn): With this section you will need to learn how to evaluate variable expressions.

Terms to Know

1. Variable-is a symbol or letter used to represent a number.

2. Algebraic expression-is a collections of numbers, variables, operations, and grouping symbols.

1-6 Writing Expressions

The following is a list of Algebraic expressions and there meanings:

Algebraic expressions

Meanings

15y 15 times y

7a

b7 times a, divided by b

3 6m 3 times m, plus 6

1-6 Writing Expressions

Next, let’s look at how to evaluate some algebraic expressions.

Example 1

Evaluate 3x + 7y when x = 4 and y = 2.

Solution: to evaluate this expression, simply substitute 4 for x and 2 for y.

3 7 3 7x y ( ) ( ) 4 2

12 14

26

First, write the expression. Then substitute 4 for x and 2 for y. Simplify 3(4) and 7(2). Then add.

SOLUTION

1-6 Writing Expressions

Let’s look at how to evaluate another algebraic expressions.

Example 2

Evaluate x + (5x - 8) when x = 3.

Solution: to evaluate this expression, simply substitute 3 for each x .

Substitute 3 for x twice.

SOLUTION

x x (5 ) (5 )8 3 3 8 3 15 8

3 710

Simplify 5·3.

Simplify 15 - 8.

1-6 Writing Expressions

Remember, to evaluate an expression use the following flow chart and show your work!!!!

Write the algebraic expression.

Substitute values for variables.

Simplify the numerical expression.

1-6 Writing Expressions

Example 3

Representing real life situations.

Recall: the Area of a rectangle is equal to the length times the width.A = lw

Suppose the length of a rectangle is 12in. and the width of the rectangle is 5in.. What is the Area of the rectangle?

Solution Use the formula A = lwA = (12in.)(5in.)= 60 sq. in.