Exercise 54 Page 796

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 formula below. C=2π r From the figure, we know that the diameter of the circle is 6.2cm. To use the formula, we first need to divide the diameter by 2 to determine the radius.

r=d/2

Substitute

d= 6.2

r=6.2/2

CalcQuot

Calculate quotient

r=3.1

By substituting 3.1 for r in the formula, we can calculate C.

C=2π r

Substitute

r= 3.1

C=2π( 3.1)

Multiply

Multiply

C=6.2π

UseCalc

Use a calculator

C=19.477874...

RoundDec

Round to 1 decimal place(s)

C ≈ 19.5

The circumference of the circle is approximately 19.5cm.

Area

Similar to the perimeter, the area of a circle with radius r is calculated using the formula below. A=π r^2 From the previous calculations, we know that the radius of the circle is 3.1cm. By substituting 3.1 for r in the formula, we can calculate A.

A=π r^2

Substitute

r= 3.1

A=π( 3.1)^2

CalcPow

Calculate power

A=π * 9.61

UseCalc

Use a calculator

A=30.190705...

RoundDec

Round to 1 decimal place(s)

A ≈ 30.2

The area of the circle is approximately 30.2cm^2.