Difference between revisions of "Quadrilateral"
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* A [[rhombus]] has four equal sides | * A [[rhombus]] has four equal sides | ||
* A [[kite]] has two pairs of adjacent equal sides | * A [[kite]] has two pairs of adjacent equal sides | ||
| − | * A [[re-entrant quadrilateral]] has one internal angle greater than 180<sup> | + | * A [[re-entrant quadrilateral]] has one internal angle greater than 180<sup>o</sup>; this may be contrasted with a [[convex quadrilateral]] in which all internal angles are less than 180<sup>o</sup> |
* An [[arrowhead]] is a re-entrant [[kite]] | * An [[arrowhead]] is a re-entrant [[kite]] | ||
* A [[square]] is both a [[rectangle]] and a [[rhombus]] | * A [[square]] is both a [[rectangle]] and a [[rhombus]] | ||
Revision as of 12:49, May 14, 2007
A quadrilateral is a polygon with four sides.
As a consequence of the definition, the sum of the angles in a quadrilateral equals 360o, 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 180o; this may be contrasted with a convex quadrilateral in which all internal angles are less than 180o
- An arrowhead is a re-entrant kite
- A square is both a rectangle and a rhombus
