Exercise 7 Page 61

Let's find the circumference and the area of the circle separately.

Circumference

The circumference C of a circle with radius r is calculated using the following formula. C=2π r We are shown that the diameter of the circle is 12.8cm. Because we have been given the diameter rather than the radius, to use the formula we first need to divide the diameter by 2. r=d/2 ⇒ 12.8/2= 6.4 By substituting 6.4 for r in the formula, we can calculate C.

C=2π r

Substitute

r= 6.4

C=2π( 6.4)

Multiply

Multiply

C=12.8 π

UseCalc

Use a calculator

C=40.212385...

RoundDec

Round to 1 decimal place(s)

C≈ 40.2

The circumference of the circle is approximately 40.2cm.

Area

Similar to the perimeter, the area of a circle with radius r is calculated using a well-known formula. A=π r^2 We know that the radius of the circle is 6.4cm. By substituting 6.4 for r in the formula, we can calculate A.

A=π r^2

Substitute

r= 6.4

A=π( 6.4)^2

CalcPow

Calculate power

A=π (40.96)

UseCalc

Use a calculator

A=128.679635...

RoundDec

Round to 1 decimal place(s)

A≈ 128.7

The area of the circle is approximately 128.7cm^2.