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**Introduction**

We live in a three-dimensional world. Every object you can see or touch has three dimensions that can be measured: lenght, widht and hight. The room you are sitting in can be described by these three dimensions. The monitor you're looking at has these three dimensions. Even you can be described by these three dimensions. In fact, the clothes you are wearing were made specifically for a person with your dimensions.

In the world around us, there are many three-dimensional geometric shapes. In these lessons, you'll learn about some of them. You'll learn some of the terminology used to describe them, how to calculate their surface area and volume, as well as a lot about their mathematical properties.

**3D Shapes**

There are many types of three-dimensional shapes. You've surely seen spheres and cubes before. In this lesson, you'll learn about polyhedra — three-dimensional shapes whose faces are polygons — and you'll also learn about two special types of polyhedra: prisms and pyramids.

Polyhedra

A die is in the shape of a cube. A portable DVD player is in the shape of a rectangular prism. A soccer ball is in the shape of a truncated icosahedron. These shapes are all examples of polyhedra.

A three-dimensional shape whose faces are polygons is known as a *polyhedron*. This term comes from the Greek words *poly*, which means "many," and *hedron*, which means "face." So, quite literally, a polyhedron is a three-dimensional object with many faces.

The faces of a cube are squares. The faces of a rectangular prism are rectangles. And the faces of a truncated icosahedron are pentagons and hexagons — there are some of each.

The other parts of a polyhedron are its edges, the line segments along which two faces intersect, and its vertices, the points at which three or more faces meet.

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