A **polygon** is a plane figure made up of
three or more line segments which intersect only at their endpoints and in which
each endpoint is on exactly two line segments.

The line segments are called the **sides** of the polygon. Each
endpoint is called a **vertex** of the polygon.

A polygon is **convex** if for any two points, A and B, in the interior of the polygon, the line segment AB is also in the
interior of the polygon.

A polygon which is not convex is called
**concave**.

Can you find two points in the interior of this polygon
such that the line segment joining them is **not** entirely in the
interior of the polygon?

Solution

A **regular** polygon is a polygon in which all the sides are equal
and all the angles are equal. For example, the equilateral triangle is a regular
polygon.

More on Regular Polygons

## More terms

A **plane figure** is a figure in a plane, that is, on a flat
surface.

A closed plane figure divides the plane into two regions, the interior and the
exterior. The **interior** is what we commonly think of as the
inside. The **exterior** is what we commonly think of as the
outside.

Return to Polyhedra