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.
|Circle of radius r|
|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|
See also: Annulus, Arc, Central Angle, Circumference, Concentric Circles, Conic Section, Cylinder, Diameter, Disc, Ellipse, Escribed Circle, Great Circle, Hemisphere, Interior of a Circle, Malfatti Circles, pi, Polygon, Radical Axis, Radical Centre, Radius, Small Circle, Sphere, Tangential.