How do you find the radius using the circumference?

The equation for circumfrance is 2(pi)r (pi meaning the constant 3.14159, rounded). To find the radius if the circumfrance is known, you would re-arrange this equation to solve for r - it would go from C=2(pi)r into r=C/2(pi).

c = circumference, r = radius.

If the circumference is 2*pi*r, then r = c/(2*pi)=