Page 663 - Basic College Mathematics with Early Integers

9.3 PERIMETER
Objectives

Use Formulas to Find Perimeter.

Use Formulas to Find Objective Using Formulas to Find Perimeters
Circumferences.
Recall from Section 1.3 that the perimeter of a polygon is the distance around the poly-
gon.This means that the perimeter of a polygon is the sum of the lengths of its sides.

PRACTICE 1 Example 1 Find the perimeter of the rectangle below.
a. Find the perimeter of the
rectangle.
5 inches

9 inches
15 meters
Solution:

perimeter = 9 inches + 9 inches + 5 inches + 5 inches
12 meters
= 28 inches
b. Find the perimeter of the
rectangular lot shown below: Work Practice 1

Notice that the perimeter of the rectangle in Example 1 can be written as
#
#
2 19 inches2 + 2 15 inches2.
c c
60 feet length width
In general, we can say that the perimeter of a rectangle is always
80 feet
#
#
2 length + 2 width
As we have just seen, the perimeters of some special figures such as rectangles
form patterns. These patterns are given as formulas. The formula for the perimeter
of a rectangle is shown next:

Perimeter of a Rectangle

#
#
perimeter = 2 length + 2 width length
In symbols, this can be written as
width width
P = 2l + 2w
length

PRACTICE 2 Example 2 Find the perimeter of a rectangle with 11 in.

Find the perimeter of a a length of 11 inches and a width of 3 in.
rectangle with a length of 3 inches.
22 centimeters and a width of Solution: We use the formula for perimeter and replace the letters by their
10 centimeters. known lengths.

P = 2l + 2w
# #
= 2 11 in. + 2 3 in. Replace l with 11 in. and w with 3 in.
= 22 in. + 6 in. Copyright 2012 Pearson Education, Inc.
= 28 in.
Answers
1. a. 54 m b. 280 ft The perimeter is 28 inches.
2. 64 cm
Work Practice 2
640