The area of a circle (A) is given by the formula A=pi*r2

where r is the circle's radius. The formula to find r is. If and, r is centimeters.

For this case what you must do is to determine the value of r of the given equation:

A = pi * r ^ 2.

Clearing the value of r we have:

r = root (A / pi)

Note that r has two roots:

r1: = + root (A / pi)

r2: = - root (A / pi)

In this case we must ignore the negative root.

Answer:

The formula to find r is

r = root (A / pi)