## Pyramids

A **pyramid** is a polyhedron with a polygonal base and with all of the other faces triangles that meet at one vertex called the **apex**. The pyramid is named according to the shape of the base.

A cone is not a pyramid because it does not have triangular side faces.

In this topic we will look at some examples of pyramids.

### Triangular-based pyramid

A triangular-based pyramid is also known as a tetrahedron. It has four faces that are all triangles.

This is the net of a regular tetrahedron. All sides are equilateral triangles.

A triangular-based pyramid has 4 faces, 4 vertices including the apex and 6 edges. To build a triangular pyramid with construction materials, we would need 4 triangles that join at the edges to make a closed three-dimensional shape or 6 edge pieces and 4 corner pieces to make a frame.