A sphere has a volume of 86.5cm3 find the radius
The volume of a sphere is given by this formula:
$$V =\frac{4}{3}pi*r^3$$
You wish to find the radius, r.
1. Divide both sides by 4pi/3:
$$\frac{3V}{4pi} = r^3$$
Take the cube root on both sides:
$$r = 3root[\frac{3V}{4pi}]$$