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.
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As a consequence of the definition, the sum of the angles in a quadrilateral equals 360<sup>0</sup>, and all quadrilaterals are capable of [[tessellation|tessellating]] an [[infinite]] plane.
===Classification of Quadrilaterals===
===Classification of Quadrilaterals===
The [[classification]] of quadrilaterals is complex, as there are several intersecting sub-categories:
The [[classification]] of quadrilaterals is complex, as there are several intersecting sub-categories:
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* 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
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* A (British) [[trapezium]] or (American) [[trapezoid]] has one pair of opposite sides parallel. A version of this called the [[isosceles trapezium]] has the other pair of opposite sides equal
* A [[parallelogram]] has two pairs of opposite sides parallel (and equal)
* A [[parallelogram]] has two pairs of opposite sides parallel (and equal)