Geometria Top, Jonathan KY, https://www.facebook.com/photo/?fbid=10215625868479449&set=gm.1094852537951781

 

aops, https://artofproblemsolving.com/community/c4h2719933p23656878

 A metrical solution for this problem: 

Problem, Ali Mohamed Mira, Geometria Top, https://www.facebook.com/photo/?fbid=2103138099840359&set=gm.1090523831717985

 

Problem Geometria Top, Ali Mohamed Mira https://www.facebook.com/photo/?fbid=2105929869561182&set=gm.1092753504828351

 

INMO 2021, problem 5, https://artofproblemsolving.com/community/c4t48f4h2719655_request_for_the_source

 

aops, Cono Sur 2017 Training List, https://artofproblemsolving.com/community/c6t48f6h2723266_ltadb__lt_cam_if_ltdab__90o_ltadc_ltbam

 

aops, Baltic Way SL 2011, https://artofproblemsolving.com/community/c6t48f6h2722119_angle_chasing_ltabd30o__ltcdb__20o_ltbca__lt_acd__40o