Polygons

A polygon is a simple, closed, planar figure composed of a finite sequence of straight line segments (called sides) connected end-to-end. The points where the sides meet are called vertices. The sides do not cross each other.

Important properties

• The number of sides (n) equals the number of vertices.

• Polygons are classified by the number of sides: triangle (3), quadrilateral (4), pentagon (5), etc.

• The sum of the interior angles of an n-sided polygon is $(n-2) \times 180^\circ$.

• A polygon is regular if all sides and all angles are equal.

• Polygons can be convex (all interior angles less than $180^\circ$) or concave (at least one angle greater than $180^\circ$).