Exercise 36 Page 720

What is the formula for finding the circumference of a circle?

Radius: 4.25in.
Circumference: 26.7in.

Practice makes perfect

Let's find the length of the radius and the circumference separately.

Diameter

To find the radius, we can divide the given diameter by 2. From the exercise, we know that the diameter of the circle is 8 12 inches. r = d/2 → r = 8 12/2Let's simplify it.

r = 8 12/2

WriteDec

Write as a decimal

r = 8.5/2

CalcQuot

Calculate quotient

r=4.25

Circumference

The circumference C of a circle with radius r is calculated using the formula below. C=2π r As we have found, the radius of the circle is 4.25 inches. By substituting it into the formula, we can calculate C.

C=2π r

Substitute

r= 4.25

C=2π( 4.25)

Multiply

C = 8.5π

UseCalc

Use a calculator

C=26.703537 ...

RoundDec

Round to 2 decimal place(s)

C≈ 26.70