Suppose you had a pizza, and you were asked to find the volume of the pizza.

Let’s assume, with huge loss of generality, that our pizza is approximately a right cylinder, and call it’s height a and it’s radius z (it’s well known that pizza’s cover everything from a to z, so this is appropriate). The area of a right cyliner is \pi * r^2 * height, which in this case is

pi * z * z * a.