November 24th, 2016, 10:55 AM  #1 
Newbie Joined: Nov 2016 From: Slovenia Posts: 24 Thanks: 0  difficult proof!
AD is an altitude in an acute triangle ABC. Points E,F are orthogonal projections of D on, respectively, AB,AC,. M,N are midpoints of, respectively, AB,AC. Lines MF,EN intersect at point S. Show that circumcenter of ABC lies on line SD. I have no idea 

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