Tangents to an Excircle
A circle drawn outside a triangle that is tangent to the extensions of two of its sides and to the third side is an excircle.[more]
Let ABC be a triangle. Construct the excircle with center O opposite A. Let D and E be the points of intersection between the line perpendicular to AO and the extensions of AB and AC. Then .[less]
The statement of the theorem is in Problem 66. Triangle, Excircle, Tangents, Geometric Mean.