Octadecagon

A octadecagon or 18-gon is a shape with 18 sides and 18 corners.
Regular octadecagon.
All sides of a regular octadecagon are the same length. Each corner is 160°. All corners added together equal 2880°.
Area.
The amount of space a regular octadecagon takes up is
The area of a regular octadecagon of side length "a" is given by