Write a formula for the area of a circle in terms of its circumference.?

Question

A=πr²

C=2πr

A step by step would be great so i can see and understand how to do this. Thanks in advance.

Answer 1

There are two equations given

A=πr²    --- call this Equation 1

C=2πr   ---  call this Equation 2

From Equation 2,

r = C/2π

and substituting this in Equation 1,

A = π(C/2π)^2

A = π(C^2/4π^2)

Simplifying,

A = C^2/(4π)

Hope this helps.

Answer 2

Equation 1) C=2πr

Equation 2) A=πr²

r = C/2π              (rearrange equation 1 to solve for r)

A = π(C/2π)²        (substitute r from equation 1 for r in equation 2)

A = C²/4π            (square and cancel π)

Answer 3

r = C/2pi

A = pi (C/2pi)^2 = pi C^2/(4 pi^2)

= C^2 / (4 pi)

Answer 4

Multiply radius by itself (i.e 10*10)

Multiply that product by Pi. That's it!

Here's another example

Bobby's circle has a radius of 28.5 cm

He finds out what 28.5*28.5 is using a calculator

(28.5*28.5)=812.25

He then multiplies 812.25 by π and gets the area of his circle, being approximately 2552.90175  where pie is 3.143, or  2550.465 where pie is 3.14 flat.

Try this

Find the area of a circle with a radius of 13.5 cm, good luck.

-Don't you learn this at school?