A **decagon** is defined as a polygon with ten sides. The word “deca” itself means “ten”. A decagon has 10 sides and 10 internal angles. It has ten vertices as well. Decagons may be irregular or regular.

**Properties of Decagon**

- Each angle in a regular decagon is equal to 144°.
- A regular decagon is one that has its 10 sides of equal length and 10 angles of equal measure.
- All sides are the same length (congruent) and all interior angles are the same size i.e congruent in case of regular decagon.
- Sum of all angles = 1440
- Number of triangles created by drawing the diagonals from a given vertex=8
- Straight sides, interior angle sum of 1440 degrees and exterior angle sum of 180 degrees, ten sides, flat, divides a plane into an inside and an outside.

**Types**

**Regular Decagons**

A regular decagon is referred as a decagon that has all 10 sides equal in length and has all 10 interior angles equal in measure. To find the measure of the central angle of a regular decagon, make a circle in the middle. A circle is 360 degrees around. Divide that by ten angles. 360^{0} / 10 = 36^{0}. So, the measure of the central angle of a regular decagon is 36 degrees.

**Irregular Decagons**

Irregular decagons are those which have unequal sides and unequal angles. Few sides or angles may be same, but all of them are not.