The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry. 
Home Analytic Geometry Quadrilateral Tangential Quadrilateral  
See also: Quadrilateral  General Definitions, Parallelogram and Rhombus, Cyclic Quadrilateral  
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Tangential QuadrilateralA 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 byA = sr, with r being the radius of the incircle.Please note that a rhombus is a special case of a tangential quadrilateral.


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