# Introduction to Pyramids

A **pyramid** is solid figure whose base is a polygon and whose sides meet at a common point. This common point is called the **vertex **or **apex** of the pyramid. The triangular sides are called the **lateral faces**. The **altitude** of a pyramid is the perpendicular distance from the vertex to the base.

A pyramid is named according to the shape of its base. A **triangular pyramid** is a pyramid that has a triangular base, a **squared pyramid** is one with a square base, etc.

A **right pyramid **or a **regular pyramid** is a pyramid whose base is a regular polygon and whose lateral faces are congruent isosceles triangles. In a regular pyramid, the **axis** (the line drawn from the vertex to the center of the base) is perpendicular to the base. Thus, in a regular pyramid, the axis and the altitude are identical. In the figure, $$OF$$ is the altitude and it shows a regular pyramid with a square base.

The **slant height** of a right pyramid is a line drawn from the vertex to the center of one edge of the base. In the figure, $$EF$$ is a slant height. A **lateral edge **is a line in which two faces meet. In the figure, $$DF$$ is a lateral edge.