Question

What information do you need in order to find the area or circumference of a circle?

Answer 1

You need to know the radius.

Answer 2

Use the formula for the area of a circle,π*r^2, or pi times radius r squared = Area A.Use the formula for the circumference of a circle, 2*π*r, or 2 times pi time radius r = Circumference C.Isolate r in the formula for the area, so divide by π, then take the square root: sqrt(A/π)