The example below illustrates clearly how to find the radius of a circle when the circumference is known. Suppose the circumference of a circle is 50.24 inches, calculate r.
Here are the steps to follow:
Write down the circumference formula.
Replace the circumference with 50.24 inches.
Since you are looking for r, you need to get rid of 2 × pi. You do this by dividing both sides by 2 × pi.
Notice that now the number next to r is just 1 and 1 times r is r. To get the answer, you just have to divide 50.24 inches by 6.28. When the circumference of a circle is 50.24 inches, the radius is 8.
Find r when the circumference is 31.4
r = 31.4 / 6.28 = 5.
Yes, it is that simple yet you still need to know how to do it by following the steps above.