Year 8 Interactive Maths - Second Edition

Polygons

Some examples of polygons are shown below.

The following figure is not a polygon as it is not a closed figure.

A circle is not a polygon as it does not have straight sides.

Polygons are named according to the number of sides.  The names of the most common polygons are given below:

Concave Polygon

If a polygon has a reflex angle, then it is said to be a concave polygon.

An example of concave polygon is shown below.

Convex Polygon

If a polygon has no reflex angle, then it is said to be a convex polygon.

Examples of the convex polygons are shown below.

Regular Polygon

A regular polygon's sides are all of the same length and its angles are the same size.

For example, a square is a regular polygon.

Examples of regular polygons are shown below.

Irregular Polygon

If a polygon is not a regular polygon, then it is said to be an irregular polygon.

For example, the quadrilateral shown below is an irregular polygon.

Key Terms

polygon, pentagon, hexagon, heptagon, octagon, nonagon, decagon, undecagon, dodecagon, concave polygon, reflex angle, convex polygon, regular polygon, irregular polygon