difficult proof! "AD is an altitude in an acute triangle ABC...."

[TobiWan]

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 just drawed it.. Any ways to begin?

 

[Steven G]

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 just drawed it.. Any ways to begin?

Can we see your diagram? Can you please tell us what an acute triangle is? How about orthogonal projection and circumcenter? We want to see that you know the definitions so we can guide you if you have something wrong. Please get back to us. Thank you

 

[TobiWan]

here