In this activity, we will decide whether a polygon is regular or irregular.

 

The word polygon comes from the Greek language:

polús means many and gõnía means angles.

 

A polygon is a flat shape with straight sides that are joined to form a closed shape. It will have several angles.

 

Regular polygons

A regular polygon is one in which all the sides are equal in length and all the interior angles are equal in size.

 

    

A square has 4 equal sides and 4 equal angles of 90°.

 

A regular pentagon has 5 equal sides and 5 equal angles of 108°.

 

 

A regular octagon has 8 equal sides and 8 equal angles of 135°.

 

 

Irregular polygons

An irregular polygon is one in which either all the sides are not equal in length and/or all the interior angles are not equal in size.

 

 

This triangle is scalene. It has sides of 3 different lengths and 3 different angles. It is irregular.

 

 

This pentagon has three 90° angles, but also two angles which are larger. The sides are of differing lengths. It is irregular.

 

Let's have a go at some questions. Remember to look carefully to see if the angles and sides are equal!