Cone

If you haven't read the section about pyramids, do that first.

Now that we've justified the formula for a pyramid, justifying the formula for a cone is quick. First, you just draw a cone and a pyramid which has the same height and the same area in their bases (the area of the circular base of the cone is the same as the area of the square base in the pyramid)

The area of the cross sections for both figures will be the same. That means we get to use Cavalieri's Principle, which means the volume of both figures is equal. Therefore, the volume equation of a cone is the same as the volume equation of a pyramid

V_pryamid = (1/3)Bh

V_cone = (1/3)Bh