The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry. 
Home Analytic Geometry Triangle Excircle of a Triangle  
See also: Altitudes of a Triangle, Incircle and Angle Bisectors of a Triangle, Circumcircle of a Triangle  
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Excircle of a TriangleThe excircle is the circle whose center is defined by the intersection of the external angle bisectors of two vertices A and B (angles α' and β'), and which is tangent to the side c between the two vertices. The excircle is also tangent to the extension of the sides a and b. Each triangle has three excircles, whose radii are determined by the following equations:
Note that the excircles are not necessarily tangent to the incircle.


Home Analytic Geometry Triangle Excircle of a Triangle 