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

Tangential Quadrilateral

A tangential quadrilateral is one for which an incircle can be constructed. This means that all four sides of the quadrilateral are tangent to the incircle.

The opposite sides of a tangential quadrilateral satisfy the following equation:

a + c = b + d = s,

with s being half of the perimeter (semiperimeter). The area of the tangential quadrilateral can be calculated by

A = sr,

with r being the radius of the incircle.

Please note that a rhombus is a special case of a tangential quadrilateral.

Last Update: 2010-12-06