A closed plane figure (shape) bounded by three or more straight-line segments. A list of names of polygons, and the formulae for finding their areas when their sides are equilateral :# sides . . .polygon . . . . .area (when s = length of side) 3 triangle 0.433 s squared 4 square s squared 5 pentagon 1.7205 s squared 6 hexagon 2.5981 s squared 7 heptagon 3.6339 s squared 8 octagon 4.8284 s squared 9 nonagon 6.1818 s squared 10 decagon 7.6942 s squared 11 undecagon 9.3656 s squared 12 dodecagon 11.1961 s squaredOther 4-sided polygons are the parallelogram (can be equilateral or non-equilateral), quadrilateral (sides can be of any lengths), rectangle (non-equilateral), and rhombus (non-equilateral), trapezium, and trapezoid (non-equilateral).Also see circle, mathematics, polyhedron, radial, regular, vertex, and wireframe.