What is the formula for finding the radius of a circle when you have the area?

Answer 1

Radius2 = A/pi

Radius = √(A/pi) (the square root of A/pi)

In other words:

1. Divide the area by pi (3.1416)
2. Get the square root of the answer.
3. That is the radius.

For example: The area is 12.5664 square centimeters.

1. Divide 12.5664 by pi (3.1416) and the answer is 4
2. Get the square root of 4, which is 2
3. The radius is 2 centimeters.

A:

A (area): A = pi.r.r

D (diameter): d = 2 x R

C (circumference): C = pi x D

Always remember: r (radius), is always half the diameter (D).

So you could simply say r = d/2.

But, what if you only had the C (circumference) to work with?

We say C = 10. Find r

C = pi x D

We know pi = 3.1416.

So, to find r (radius). 10 = pi x D

10 = 3.146 x D

D = 10/3.146

D = 3.179

Since r (radius) is always half of D (Diameter)... We now have D. Go figure ;)