Polygon

Each face of a polyhedron is a polygon.

A nonagon, sometimes called an enneagon, is a polygon with nine sides.

A seven-sided polygon is typically called a heptagon, but is occasionally referred to as a septagon.

Calculate the area of this polygon.

Mathematicians have finally discovered an aperiodic monotile, that is, a polygon that can only tile the plane in aperiodic tessellations.