Polygons are closed figures made up of at 3 or more lines. Polygons are classified according to the number of sides they have. 3 sides = triangle 4 sides = quadrilateral 5 sides = pentagon 6 sides = hexagon 7 sides = heptagon 8 sides = octagon 9 sides = nonagon 10 sides = decagon 11 sides = hendecagon 12 sides = dodecagon Regular polygons are those in which all sides are congruent. The sum of the internal angles of a polygon can be found with the following formula: 180(n  2)
