Decagon

A polygon with 10 sides

In a deck of cards the highest number is a 10 (Dec has the same word root as decade which is 10 years).

Example 1

All 10 sides of a regular decagon are equal in length.

Example 2

The internal angle between the sides of a regular decagon is 144°.

Example 3

An irregular decagon such as the one above may be convex as in this case.

Example 4

The decagon above is an irregular concave decagon.

Example 5

This star shape is an irregular decagon as the internal angles between the sides are not all equal.