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