# What is a pentagonal prism?

Written by lynn wood
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A pentagonal prism is a three-dimensional box whose bottom and top have five sides instead of the normal four. This means that the box also has five sides instead of the typical four. The Pentagon Building in Washington, D.C., is an example of a pentagonal prism.

## Prisms

Prisms are three-dimensional boxes with two similar bases. The most recognisable prism has square or rectangular bases making it look like your typical box. A prism can have triangular bases giving it three sides, pentagonal bases giving it five sides, hexagonal bases giving it six sides, and so on.

## Pentagons

A pentagon is a five-sided polygon, just like a square is a four-sided polygon and a triangle is a three-sided polygon. If all five sides are equal or the same length, the figure is called a regular pentagon.

## Volume

The most common calculation made on a pentagonal prism is to find its volume. To find the volume of any prism, you must multiply the area of the base of the prism by its height. To find the volume of a regular, pentagonal prism you need to know the apothem length (a), which is the measure from the centre of the pentagon to the midpoint of any side, the length of any side (s), and the height (h) of the prism. You multiply (a)(s)(h)(5/2).

## Surface Area

The second most common calculation made on a pentagonal prism is to find its surface area. To find the surface area of a pentagonal prism you need the same three numbers a, s, and h as you did for the volume. Multiply 5(a)(s) together and 5(s)(h) together and then add the two numbers.

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