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inscribed circle

Source: China south east mathematical Olympiad 2012 day1 problem 2

July 17, 2013
geometrycircumcircletrigonometrygeometry unsolved

Problem Statement

The incircle II of ABC\triangle ABC is tangent to sides AB,BC,CAAB,BC,CA at D,E,FD,E,F respectively. Line EFEF intersects lines AI,BI,DIAI,BI,DI at M,N,KM,N,K respectively. Prove that DMKE=DNKFDM\cdot KE=DN\cdot KF.