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Home Mathematics Analytic Geometry Quadrilateral Quadrilateral - General Definitions
See also: Triangle - General Definitions, Trapezoid, Rectangle and Square, Parallelogram and Rhombus, Varignon Parallelogram, Tangential Quadrilateral, Cyclic Quadrilateral, Kite 

Quadrilateral - General Definitions

A quadrilateral is a four-sided polygon, which is sometimes also called "quadrangle" or "tetragon". All four vertices of the quadrilateral have to lie on a plane, otherwise it is called a "skew quadrilateral".

One can differentiate between three topologies: convex quadrilaterals (left figure), concave quadrilaterals, and crossed quadrilaterals.

The sum of the angles in a (non-crossed) quadrilateral is 360°:

a + b + g + d = 360.

The area A of a quadrilateral is given by

A = 0.5d1d2sin j

The angle j between the diagonals d1 and d2 is

j = (a + g)/2 = (b + d)/2


Last Update: 2005-Aug-17