A octadecagon or 18-gon is a shape with 18 sides and 18 corners.

All sides of a regular octadecagon are the same length. Each corner is 160°. All corners added together equal 2880°.

The amount of space a regular octadecagon takes up is

The area of a regular octadecagon of side length a is given by

${\displaystyle A={\frac {18}{4}}a^{2}\cot {\frac {\pi }{18}}\simeq 25,5208a^{2}}$

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