Question

The circumference of a circle is 9π m. What is the area, in square meters? Express your answer in terms of π

Answer 1

`20.25\pi\:\mathrm{m^2}`

Explanation:

Formulas to know:

• Area of a circle:
  `A=r^2\pi`
• Circumference of a circle:
  `C=2r\pi`

Since we know the circumference, we can use formula for the circumference of a circle to find the circle's radius:

`9\pi=2r\pi,\\9=2r,\\r=4.5`

Now we can plug in
`r=4.5` into the formula for an area of a circle:

`A=4.5^2\pi=\boxed{20.25\pi\:\mathrm{m^2}}`

Answer 2

20.25 pi

Explanation:

The circumference of a circle is given by

C = 2 * pi *r

9 pi = 2 * pi *r

Divide each side by 2pi

9pi / 2 pi = 2 pi r / 2 pi

4.5 = r

Now we can find area

A = pi r^2

= pi ( 4.5)^2

20.25 pi