# What Is a Polygon? (Mathematics Glossary)

# What Is a Polygon?

A polygon is a 2-dimensional shape with straight sides.# Regular Polygons

Regular polygons have equal sides and equal angles.Shape | Name | Number of sides |
---|---|---|

Triangle(or Trigon)A regular triangle is an equilateral triangle |
3 | |

Quadrilateral(or Tetragon)A regular quadrilateral is a square |
4 | |

Pentagon | 5 | |

Hexagon | 6 | |

Heptagon | 7 | |

Octagon | 8 | |

Nonagon | 9 | |

Decagon | 10 | |

Dodecagon | 12 |

# Irregular Polygons

Irregular polygons have different length sides and different angles.Shape | Name | Number of sides |
---|---|---|

Irregular Quadrilateral | 4 | |

Irregular Hexagon | 6 | |

Irregular Octagon | 8 |

# More About Polygons

The slider below shows more information about polygons.##### Curriculum

##### Interactive Test

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##### Note

**WHAT'S IN A NAME?**

Polygon comes from the Greek 'poly-', meaning "many", and '-gon', meaning "angle".

Therefore 'polygon' means "many angles" as each polygon has several angles inside of it.

# INTERIOR ANGLES

The angles between the sides in a polygon, inside the shape, are called interior angles.There is a formula for the sum of the interior angles of a polygon:

where

**n**is the number of sides of the polygon.

For example, a

**hexagon**has

**6**sides, so

**n = 6**. Putting this into the forula gives:

(n - 2) × 180° =

(6 - 2) × 180° =

4 × 180° =

720°

The angles in a hexagon add up to 720°

# EXTERIOR ANGLES

The angles between the sides in a polygon, outside the shape, are called exterior angles.The exterior angles always add up to 360°.