Exercise 93 Page 521

Use the formulas for finding the area and circumference of a circle.

Area: about 132.73 square millimeters
Circumference: about 40.84 centimeters

We want to find the the circumference and the area of the circle with a radius of 6.5 centimeters. We can do each of these things one at a time.

Area

Let's represent the situation on a diagram!

Notice that the circle has the diameter of 6.5 centimeters. Now, we can recall formula for the area A of a circle with radius r. A=π r^2 Let's substitute 6.5 for r in the formula and calculate A!

A=π r^2

Substitute

r= 6.5

A=π( 6.5)^2

CalcPow

Calculate power

A=π(42.25)

UseCalc

Use a calculator

A=132.732289...

RoundDec

Round to 2 decimal place(s)

A≈ 132.73

The area of the circle is about 132.73 square centimeters.

Circumference

Now, we can calculate the circumference of the circle. Let's recall the formula for the circumference C of a circle with radius r. C=2π r Let's substitute 6.5 for r in the formula and calculate C!

C=2π r

Substitute

r= 6.5

C=2π( 6.5)

Multiply

C=13π

UseCalc

Use a calculator

C≈ 40.840704...

RoundDec

Round to 2 decimal place(s)

C≈ 40.84