# Prism

## Prism

Polyhedron bounded by two parallel and congruent polygons, called the bases of the prism, that are joined by parallelograms that form the lateral surface of the prism.

The figure below illustrates the different elements of a prism:  • The two parallel planes that cut the generatrices of a prismatic surface form two congruent polygons called the bases of the prism.
• Each of the two polygonal chains where the prismatic surface and the two parallel planes meet is called the directrix of the prism.
• The height of a prism is the distance between the two bases of a prism.
• The length of a right rectangular prism is the longest dimension of its base.
• A prism is a right prism when its generatrices are perpendicular to its bases; otherwise, it is an oblique prism.

### Properties

A prism is named according to its bases:

• If the bases of a prism are squares, it is a square prism;
• If the bases of a prism are triangles, it is a triangular prism;
• If the bases of a prism are pentagons, it is a pentagonal prism;
• If the bases of a prism are hexagons, it is a hexagonal prism.

If the bases of a right prism are regular polygons, then the prism is a regular prism.

Many everyday objects have the shape of a prism: cereal box, tissue box, packaging box, filing cabinet, piece of cheese, building, etc.

### Examples

Examples of prisms:     These polyhedra are not prisms:     