Question

If a circle has a circumference of 81 pi what is its radius and area?

Answer 1

Solution :-

`\sf Circumference = 2\pi r`

`\sf \: 81 \pi = 2\pi r`

`\sf \: 81 = 2r`

`\sf (81)/(2) = r`

`\sf \: 40.5 = r`

Area = πr²

`\sf \: Area = 3.14 * 40.5 * 40.5`

`\sf \: Area = 5150.38`

`\sf \: Area = 5150.38 \: units {}^(2)`

Answer 2

r = 40.5

A = 1640.25 pi

Explanation:

The circumference is given by

C = pi *d

81 pi = pi *d

Divide each side by pi

81 = d

We can find the radius

d = 2r

81 = 2r

Divide each side by 2

81/2 = r

40.5

Now we can find the area

A = pi r^2

A = pi ( 40.5)^2

A =1640.25 pi