Height From the Slant

The slant height rule works in either direction. If you know the slant height and the base edge, it gives the height, and the height is what a volume needs.

This pyramid has base edge 16, so half of it is 8, and its slant height is 10. The rule says ${10}^{2} = {h}^{2}+{8}^{2}$, so ${h}^{2} = 100-64 = 36$ and the height is 6. You subtract this time, because the slant height is the hypotenuse.

On the figure the height is marked ?. Tap it and pick Slant height: the engine solves the rule for the height.