In geometry, a hendecagon is an 11-sided polygon. Undecagon is incorrect — the prefix is properly Greek, not Latin. A regular hendecagon has internal angles of 147.272727... degrees. The area of a regular hendecagon with side length a is given by

$A\; =\; \backslash frac\{11\}\{4\}a^2\; \backslash cot\; \backslash frac\{\backslash pi\}\{11\}\; \backslash simeq\; 9.36564\; a^2.$

The Canadian dollar coin, the Loonie, is a hendecagon. The interior design of the (US coin) Susan B. Anthony silver dollar is also a hendecagon.

The Indian Two-Rupee Coin is also a hendecagon.

Polygons