The circumference of a circle, given the radius, is given by . So if you are given the circumference you can find the radius by
The area of a circle is given by
Since you start with the circumference, just substitute:
Plug in your given number and do the arithmetic. Hint: Leave your answer in terms of for an exact answer. If you want a numerical approximation, 3.14 is usually close enough, but 3.14159 can be used if you want greater precision. is only off by 1 in the 3rd decimal place, and is good to six places.
John
My calculator said it, I believe it, that settles it
