How do you find the diamter of a circle if you know the area?

In order to find the diameter of a circle if you have the area is to rearrange the formula for the area of a circle to put diameter as the unknown, like so:

PIE*d = Area of a Circle

d = (Area of a Circle) / PIE

Therefore if the area of your circle is 40cm, 40/PIE = 12.73cm and that's the diameter.