Prisms are solids (three-dimensional figures) that, unlike planar figures, occupy space. They come in many shapes and sizes. Every prism has the following characteristics:

• Bases: A prism has two bases, which are congruent polygons lying in parallel planes.

• Lateral edges: The lines formed by connecting the corresponding vertices, which form a sequence of parallel segments.

• Lateral faces: The parallelograms formed by the lateral edges.

A prism is named by the polygon that forms its base, as follows:

• Altitude: A segment perpendicular to the planes of the bases with an endpoint in each plane.

• Oblique prism: A prism whose lateral edges are not perpendicular to the base.

• Right prism: A prism whose lateral edges are perpendicular to the bases. In a right prism, a lateral edge is also an altitude.

In Figure 1 , prism (a) is a right triangular prism, prism (b) is a right rectangular prism, and prism (c) is an oblique pentagonal prism. The altitude in prism (c) is called h.

Figure 1 Different types of prisms.

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