If the circumference of a circle is 40π, what is the radius of the circle?
There are two ways to do this problem. Unfortunately, both of them involve dealing with that nasty little pi symbol.
Way 1: We know C = 2πr. We can substitute the value 40π for C to get the equation 40π = 2πr, which we can solve to find that r = 20.
Way 2: In the previous example, we solved the formula C = 2πr for r to get the new formula .
If we evaluate this new formula for C = 40π, we also find that r = 20.