Hendecagon

A hendecagon or undecagon or 11-gon is a shape with 11 sides and 11 corners.

All sides of a regular hendecagon are the same length. Each corner is 147.27°. All corners added together equal 1619.97°.

The amount of space a regular hendecagon takes up is

${\displaystyle \alpha ={\frac {(n-2)}{n}}\cdot 180^{\circ }={\frac {9}{11}}\cdot 180^{\circ }\approx 147{,}273^{\circ }}$

${\displaystyle A={\frac {11}{4}}a^{2}\cot {\frac {\pi }{11}}\approx 9,36564a^{2}\,}$

a is the length of one of its sides.