Basic Mathematics for College Students

792 Chapter 9 An Introduction to Geometry

106. CARPENTRY If it costs $90 per square foot to
     build a one-story home in northern Wisconsin, find
     the cost of building the house with the floor plan
     shown below.

WRITING

107. Explain the difference between perimeter and area.


108. Why is it necessary that area be measured in square
     units?


109. A student expressed the area of the square in the
     figure below as 25^2 ft. Explain his error.

5 ft

5 ft

12 ft

30 ft

20 ft

14 ft

110. Refer to the figure below. What must be done before
     we can use the formula to find the area of this
     rectangle?

REVIEW

Simplify each expression.

111. 
     
     
     
     112. 
          
     
     
     
     


112. 
     
     
     
     114. 
          
     
     
     
     


113. 
     
     
     
     116. 
          
     
     
     
     


114. 
     
     
     
     118. 72 a
     
     
     
     

7

8

f

8

9

60 a b

3

20

r

4

15

b



5

18

x

7

18

 x

7

16

x

3

16

x

1

2

 (2y8)

2

3

(3w6)

27 a

2

3

8 a mb

3

4

tb

6 ft

12 in.

SECTION 9.8

Circles

Objectives

1 Define circle, radius, chord,

diameter, and arc.

2 Find the circumference of a

circle.

3 Find the area of a circle.

In this section, we will discuss the circle, one of the most useful geometric figures of all.

In fact, the discoveries of fire and the circular wheel are two of the most important

events in the history of the human race. We will begin our study by introducing some

basic vocabulary associated with circles.

1 Define circle, radius, chord, diameter, and arc.

Circle

A circleis the set of all points in a plane that lie a fixed distance from a point

called its center.

© iStockphoto.com/Pgiam

A segment drawn from the center of a circle to a point on the circle is called a

radius.(The plural of radiusis radii.) From the definition, it follows that all radii of the

same circle are the same length.