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Circle - Wikipedia, the free encyclopedia
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Circle
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This article is about the shape and mathematical concept. For other uses, see

Circle (disambiguation).

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Circle illustration showing a radius, a diameter, the centre and the circumference

Tycho crater, one of many examples of circles that arise in nature.

NASA photo
A circle is a simple

shape of

Euclidean geometry consisting of those

points in a

plane which are equidistant from a given point, the

centre.
Circles are simple closed

curves which divide the

plane into two regions, an

interior and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is the former and the latter is called a

disk.
A circle is a special

ellipse in which the two

foci are coincident and the

eccentricity is 0. Circles are

conic sections attained when a

right circular cone is intersected with a plane perpendicular to the axis of the cone.

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