# Difference between revisions of "Quadrilateral"

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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 | + | 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: | ||

− | * A (British) [[trapezium]] or (American) [[trapezoid]] has one pair of opposite sides parallel. A version of this called the [[ | + | * 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) | ||

* A [[rectangle]] has four right angles | * A [[rectangle]] has four right angles |

## Revision as of 05:10, 14 May 2007

A quadrilateral is a polygon with four sides.

As a consequence of the definition, the sum of the angles in a quadrilateral equals 360^{0}, and all quadrilaterals are capable of 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 isosceles trapezium has the other 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
^{0} - An arrowhead is a re-entrant kite
- A square is both a rectangle and a rhombus