Help with Replacing formulas?

Question

The formula for the area of a circle is A = pi radius squared. The formula for the circumference of a circle is C = 2 pi radius.

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

HELP please

Answer 1

A = πr^2

C = 2πr

get 2πr to equal πr^2 by first squaring both sides:

C^2 = 4 * π^2 * r^2

Now divide by 4π

C^2/4π = πr^2

so, A = C^2 / 4π