Given a convex polygon **R**contained in a plan , and a point **V** (vertex) out of we call *pyramid* the set of all segments .

## Pyramid Elements

Given the following pyramid, we have the following elements:

base: the convex polygon

**R**.base edges: the sides of the polygon.

side edges: the segments .

side faces: the triangles VAB, VBC, VCD, VDE, VEA.

height: distance

**H**of the point**V**to the plan.

## Classification

A pyramid is straight when the orthogonal projection of the vertex coincides with the center of the base polygon. Every straight pyramid whose base polygon is regular receives the name of *regular pyramid.* It can be triangular, quadrangular, pentagonal, etc., as its base is respectively a triangle, a quadrangle, a pentagon, etc. Look:

**Comments:**

1st) Every triangular pyramid is named after the tetrahedron. When the tetrahedron has equilateral triangles as faces, it is called regular (all faces and all edges are congruent).

2nd) The base-based assembly of two regular square-base pyramids results in an octahedron. When the faces of the pyramids are equilateral triangles, the octahedron is regular.