# Circle

## Simple curve of Euclidean geometry / From Wikipedia, the free encyclopedia

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This article is about the shape and mathematical concept. For other uses, see Circle (disambiguation).

"360 degrees" and "360°" redirect here. For other uses, see 360 degrees (disambiguation).

A **circle** is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. The distance between any point of the circle and the centre is called the radius.

**Quick Facts**Type, Symmetry group ...

Circle | |
---|---|

Type | Conic section |

Symmetry group | O(2) |

Area | πR^{2} |

Perimeter | C = 2πR |

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The circle has been known since before the beginning of recorded history. Natural circles are common, such as the full moon or a slice of round fruit. The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy and calculus.