# Geometry Problem 426: Triangle, Circumradius, Circumcenter, Concurrent Cevians

 The figure shows a triangle ABC with circumcenter O and circumradius R. The cevians AD, BE, and CF are concurrent at O. Prove that $$\dfrac{2}{R}=\dfrac{1}{AD}+\dfrac{1}{BE}+\dfrac{1}{CF}$$ .
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