The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry.

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:

α + β + γ + δ = 360.

The area A of a convex planar quadrilateral is given by

Last Update: 2011-01-11