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A quadrilateral is a [[polygon]] with four sides.
A quadrilateral is a [[polygon]] with four sides.
As a consequence of the definition, the sum of the angles in a quadrilateral equal 360<sup>0</sup>, and all quadrilaterals are capable of [[tessellation|tessellating]] an [[infinite]] plane.
===Classification of Quadrilaterals===
The [[classification]] of quadrilaterals is complex, as there are several intersecting sub-categories:
* A (British) [[trapezium]] or (American) [[trapezoid]] has one pair of opposite sides parallel. A version of this called the [[isoceles trapezium]] also has one pair of opposite sides equal
* A [[parallelogram]] has two pairs of opposite sides parallel (and equal)
* A [[rectangle]] has four right angles
* A [[rhombus]] has four equal sides
* A [[kite]] has two pairs of adjacent equal sides
* A [[re-entrant quadrilateral]] has one internal angle greater than 180<sup>0</sup>
* An [[arrowhead]] is a re-entrant [[kite]]
* A [[square]] is both a [[rectangle]] and a [[rhombus]]
[[Category:Geometry]]
[[Category:Geometry]]