The formula for the circumference of a circle is: c = 2πr Solve for the radius, r, by dividing both sides by 2π. What is the formula for the radius of a circle in terms of the circumference? r = 2 pi c r = StartFraction c Over 2 pi EndFraction r = StartFraction pi Over 2 c EndFraction r = StartFraction 2 pi Over c EndFraction