Youtube channel of Hasan Ata, https://www.youtube.com/watch?v=WWBojQ49yXM

 

General Problem - Triple Angle Lemma, of youtube channel of Hasan Ata, https://www.youtube.com/watch?v=wUjgygA74ZQ&t=499s

 

FB page of Hasan Ata, https://www.facebook.com/photo?fbid=24493817836941249&set=a.712949622121404

 

https://artofproblemsolving.com/community/q1h3685566p36051307

 Let ABC be an isosceles triangle (AB = AC), D projection of C onto AB and M midpoint of CD. Let K and L be projections of A onto BM and CK respectively. Prove:
1) - AL<=AB/3
2) - Gasiti conditia de egalitate.

Thiago Durado, https://www.facebook.com/photo?fbid=1110241861276771&set=gm.1872516827478191&idorvanity=1224788368917710

 

Hasan Ata, https://www.facebook.com/photo?fbid=24890699490586413&set=a.712949622121404

 

By Erdem Balkan(?)