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Circle  Defined by a set of points equidistant from a given point (the centre) that form the circumference. The diameter is a chord that passes through the centre of the circle. The radius is any line from the centre to the circumference and so is half the length of the diameter.
| Segment of a circle of radius r |  | 
| | Sector of a circle of radius r |  |  
| | Radius of a circle circumscribing a triangle of sides a, b, c |  |  
| | Radius of a circle inscribed in a triangle of sides a, b, c |  |  -
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See also: Annulus, Circumference, Conic Section, Cylinder, Diameter, Disc, Ellipse, Great Circle, Hemisphere, Interior of a Circle, pi, Polygon, Radius, Small Circle, Sphere.
  
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