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{{short description|Slice of a circle cut perpendicular to the radius}}
[[Image:Circularsegment.svg|frame|right|A circular segment (in green) is enclosed between a secant/chord (the dashed line) and the arc whose endpoints equal the chord's (the arc shown above the green area).]]▼
In [[geometry]], a '''circular segment''' (symbol: <span style="font-size:1.5em">⌓</span>), also known as a '''disk segment''', is a [[region (geometry)|region]] of a [[disk (mathematics)|disk]] which is "cut off" from the rest of the disk by a [[secant line|secant]] or a [[chord (geometry)|chord]]. More formally, a circular segment is a region of [[two-dimensional space]] that is bounded by a [[circular arc]] (of less than π radians by convention) and by the [[circular chord]] connecting the endpoints of the arc.
== Formulae ==
▲[[Image:Circularsegment.svg|frame|right|A circular segment (in green) is enclosed between a secant/chord (the dashed line) and the arc whose endpoints equal the chord's (the arc shown above the green area).]]
Let ''R'' be the [[radius]] of the arc which forms part of the perimeter of the segment, ''θ'' the central angle subtending the arc in [[radian]]s, ''c'' the [[chord length]], ''s'' the [[arc length]], ''h'' the [[Sagitta (geometry)|sagitta]] ([[Height#In mathematics|height]]) of the segment, and ''a'' the [[area]] of the segment.
Usually, chord length and height are given or measured, and sometimes the arc length as part of the perimeter, and the unknowns are area and sometimes arc length. These can't be calculated simply from chord length and height, so two intermediate quantities, the radius and central angle are usually calculated first.
=== Radius and central angle ===
The radius is:
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