# Polygons

A polygon is a closed figure where the sides are all line segments. Each side must intersect exactly two others sides but only at their endpoints. The sides must be noncollinear and have a common endpoint.

A polygon is usually named after how many sides it has, a polygon with n-sides is called a n-gon. E.g. the building which houses United States Department of Defense is called pentagon since it has 5 sides.

Sides Polygon

3 triangle

4 quadrilateral

5 pentagon

6 hexagon

7 heptagon

9 nonagon

10 decagon

A regular polygon is a polygon in which all sides are congruent and all the angles are congruent.

**Video lesson:** Determine whether the figures are
polygons or not

**Proof, Conjecture**