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# Tridecagon

In geometry, a tridecagon (or triskaidecagon) is a polygon with 13 sides and angles.

A regular tridecagon is represented by SchlĂ¤fli symbol {13}.

Regular tridecagon

The measure of each internal angle of a regular tridecagon is approximately 152.308 degrees, and the area with side length a is given by

A = \frac{13}{4}a^2 \cot \frac{\pi}{13} \simeq 13.1858\,a^2.

Numismatic use

The regular tridecagon is used as the shape of the Czech 20 korun coin.[1]

Petrie polygons

The regular tridecagon is the Petrie polygon 12-simplex:

References

Colin R. Bruce, II, George Cuhaj, and Thomas Michael, 2007 Standard Catalog of World Coins, Krause Publications, 2006, ISBN 0896894290, p. 81.

External links

Weisstein, Eric W., "Tridecagon", MathWorld.

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