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Problem 68.
Triangle, Incircle, Inradius, Tangent.
Level: High School, SAT Prep, College 
In the figure below, r is the inradius
of a triangle ABC, d is the radius of circles D and E
tangent to the angles A and C respectively, and m = AF + CG.
Prove that: \(r = \dfrac{b \cdot d}{m}\).


