A pyramid has a polygon base and triangular faces meeting at one apex. Egypt's pyramids have a square base; the Louvre's has a glass one; a triangular pyramid (tetrahedron) is the simplest of all.
Volume of any pyramid
V = ⅓ × base-area × height
Same one-third rule that the cone obeys.
Named pyramids
- Tetrahedron — triangular base. The smallest possible polyhedron — every face is a triangle.
- Square pyramid — square base. The shape of the Egyptian pyramids and the Louvre.
- Pentagonal pyramid — pentagon base. Five triangular faces.