Basic Mathematics for College Students

830 Chapter 9 An Introduction to Geometry

Find the area of the circle shown here. Give

the exact answer and an approximation to the

nearest tenth.

Since the diameter is 28 meters, the radius is

half of that, or 14 meters.

This is the formula for the area of a circle.

Substitute 14 for r,the radius of the circle.

Evaluate the exponential expression.

Write the product so that pis the last factor.

The exact area of the circle is 196pm^2. We can use a calculator to

approximate the area.

Use a calculator to do the multiplication.

To the nearest tenth, the area is 615.8 m^2.

A615.7521601

 196 p

p(196)

Ap( 14 )^2

Apr^2

The areaof a circle is given by the formula

Apr^2

28 m

To find the area of an irregular shape, break it up into

familiar figures.

To find the area of the shaded figure

shown here, find the area of the triangle

and the area of the semicircle, and then

add the results.

Ashaded figureA triangleA semicircle

86. Find the area of a circle with a diameter of 18 inches.
    Give the exact answer and an approximation to the
    nearest hundredth.


87. Find the area of the figure shown in Problem 85.
    Round to the nearest tenth.


88. Find the area of the shaded
    region shown on the right.
    Round to the nearest tenth.

100 in.

100 in.

REVIEW EXERCISES

O

A

B

D

83. Refer to the figure. C
    a. Name each chord.

b. Name each diameter.

c. Name each radius.

d. Name the center.

84. Find the circumference of a circle with a diameter of
    21 feet. Give the exact answer and an approximation
    to the nearest hundredth.


85. Find the perimeter of the figure shown below.
    Round to the nearest tenth.

8 cm

10 cm

10 cm