Suppose the area of a circle is 9pi. What is its diameter?

Formula:

A = pi * r^2

Plug in what we know:

9 pi = pi * r^2

Divide pi to both sides:

9 = r^2

Find the square root of both sides:

r = 3

So the radius is 3, and the diameter is twice the radius, so multiply by 2.

3 * 2 = 6

So the diameter is 6.

You would have to divide 9 by 3.14, also known as pi to get the diameter because the way you find area is radius squared times 3.14 and once you find the radius squared, you can divide by its root number and add it to find the diameter.