Kazakhstan finals, 2021, https://artofproblemsolving.com/community/c4t48f4h2727784_ltmka_square_abcd_ltbamltckm30o_2nd_matol_202122_kazakhstan_finals_73

 

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

 

Generalized problem of Geometria Top, Hajj Mustafa El-Rardini, https://www.facebook.com/photo/?fbid=6710749308942650&set=gm.1087931558643879

A piece of my book, 'Rose thorns - Geometry jewels', I called it 'Triple angle lemma'. The proof is mine.

 

Nelson Tunala, Geometria Top, https://www.facebook.com/photo/?fbid=3907884295946685&set=gm.962288931208143

 

Nelson Tunala, Geometria Top, https://www.facebook.com/photo/?fbid=3914651885269926&set=gm.963789431058093

 

Stanford Li, Training Geometry Olympiad, https://www.facebook.com/photo?fbid=10224737947489560&set=gm.582578046335846

 A synthetic solution:

Mongolian SL 2000 Math Olympiad, https://www.facebook.com/photo?fbid=4456586367743139&set=gm.1744931542378025

 

aophttps://artofproblemsolving.com/community/c6t48f6h2483365_amxcp__bnxdq_is_constant_projections_of_square_on_tangents,

 

Abdilkadir Altintas, Geometria Top, https://www.facebook.com/photo?fbid=3025600111102321&set=gm.1076995453070823