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Generally, the word polygon is used to refer to a two dimensional construction that encloses a space using straight lines. Regular polygons have sides that are of equal length and have equal angles between each side. Concave polygons have at least one internal angle that is greater than 180°, whereas convex polygons have all internal angles less than 180°. A cyclic polygon has all of its vertexes lying on the same circle. A polygon can belong to several classifications simultaneously; a square is a regular, convex, cyclic polygon, for example.

'Poly-' is from the Greek word for 'many' and '-gon' is a Greek combining form meaning 'angle'. Strictly speaking, every polyhedron is also a polygon as is every polytope, since they all have angles.

Regular Polygons

Name Sides Angle*
Triangle 3 60°
Square 4 90°
Pentagon 5 108°
Hexagon 6 120°
Septagon 7 128.57°
Octagon 8 135°
Nonagon 9 140°
Decagon 10 144°
Hectagon 100 176.4°
Megagon 106 180.° (approx.)
Googolgon 10100 180.° (approx.)
* Angle= 180°-(360°/ Sides )