A prism is a polyhedron, or three-dimensional figure, that has congruent polygons as bases and has parallelograms (often rectangles, for our situations) for lateral face. Prisms are the same size and shape from one base to the other.

Prisms are named by the shape of their base(s).

For Example

There is a rectangular prism on the left and a triangular prism on the right. For both prisms, the bases are the top and bottom of the figures.

If you make a cut through the prism parallel to the bases, and look at the end of your slice, you would see a cross-section congruent to the bases. All cross-sections are congruent polygons that are congruent to the bases, or top and bottom.

The rectangular prism on the left has been sliced horizontally to create a cube on top and a smaller prism on bottom.

Triangular Prisms

The triangular prism on the left has a base on bottom, and the triangular prism on the right has a lateral face on bottom.

Occasionally a prism, such as the one below, will be sitting on one of its lateral faces rather than on one of its bases, as in Figure 4. Being on its side does not change the fact that the triangles are still the bases of this prism. The rectangles are still the lateral faces.

The triangular prism in Figure five rests on its base, and Figures six and seven show cross-sections of the triangular prism.

For a triangular prism, all cross-sections are triangles that are congruent to the bases.

Nets of Prisms

The net of a triangular prism is on the left, and the net of a cube is on the right.

The nets of a square prism, pentagonal prism, and hexagonal prism are shown.

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