Hendecagon

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

<math>A = \frac{11}{4}a^2 \cot \frac{\pi}{11} \simeq 9.36564 a^2.<math>

A regular hendecagon is not constructible with straightedge and compass.

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.

See also

• geometry