Basic Mathematics for College Students

Chapter 9 Summary and Review 829

78.

79. The area of a parallelogram is 240 ft^2. If the length
    of the base is 30 feet, what is its height?


80. The perimeter of a rectangle is 48 mm and its width
    is 6 mm. Find its length.

15 m

10 m

4 m

81. FENCES A man wants to enclose a rectangular
    front yard with chain link that costs $8.50 a foot
    (the price includes installation). Find the cost of
    enclosing the yard if its dimensions are 115 ft by
    78 ft.


82. LAWNS A family is going to have artificial turf
    installed in their rectangular backyard that is 36 feet
    long and 24 feet wide. If the turf costs $48 per
    square yard,and the installation is free, what will
    this project cost? (Assume no waste.)

The circumference(perimeter) of a circle is given by

the formulas

or

where p3.14159....

CpD C 2 pr

Find the circumference of the circle shown here.

Give the exact answer and an approximation.

SECTION 9.8 Circles

A circleis the set of all points in a plane that lie a

fixed distance from a point called its center.The fixed

distance is the circle’s radius.

A chordof a circle is a line segment connecting two

points on the circle.

A diameteris a chord that passes through the circle’s

center.

Any part of a circle is called an arc.

A semicircleis an arc of a circle whose endpoints are

the endpoints of a diameter.

DEFINITIONS AND CONCEPTS EXAMPLES

A

O

E

B

C

D

Diameter

CD

Chord

AB

Radius

OE

Arc AB

Semicircle CED

8 in.

This is the formula for the circumference of a circle.

Substitute 8 for r,the radius.

Rewrite the product so that Pis the last factor.

Do the first multiplication: 2(8) 16. This is the

exact answer.

The circumference of the circle is exactly 16pinches. If we replace

pwith 3.14, we get an approximation of the circumference.

Substitute 3.14 for P.

Do the multiplication.

The circumference of the circle is approximately 50.2 inches.

We can also use a calculator to approximate 16p.

C50.26548246

C50.24

C16(3.14)

C 16 P

C 16 p

C2(8)p

C 2 p( 8 )

C 2 pr

If an exact answer contains p, we can use 3.14 as an

approximation, and complete the calculations by hand.

Or, we can use a calculator that has a pi key to find

an approximation.

p