Mammoth Memory


A polygon with 10 sides

A decagon has 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

A regular decagon has 10 equal sides

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


Example 2

A decagon has 10 vertices with an individual angle of 144 degrees 

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


Example 3

This is irregular but is still a decagon

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


Example 4

This is an irregular concave decagon

The decagon above is an irregular concave decagon.


Example 5

A star is a decagon but it is irregular

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

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