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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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