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Article: circle
- Article from:
- The Columbia Encyclopedia, Sixth Edition
CopyrightThe Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press. (Hide copyright information)
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circle closed plane curve consisting of all points at a given distance from some fixed point, called the center. A circle is a
conic section
cut by a plane perpendicular to the axis of the cone. The term
circle
is also used to refer to the region enclosed by the curve, more properly called a circular region. The radius of a circle is any line segment connecting the center and a point on the curve; the term is also used for the length
r
of this segment, i.e., the common distance of all points on the curve from the center. Similarly, the circumference of a circle is either the curve itself or its length of
arc
. A line segment whose two ends lie on the circumference is a chord; a ...