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(?)

 

A problem with lost source again!

 

FB page of Hasan Ata, https://www.facebook.com/photo?fbid=24836505739339122&set=a.712949622121404

 

Erdem Balkan, Geometria Super Top, https://www.facebook.com/photo?fbid=24484846594549583&set=gm.2065417674228591&idorvanity=830782544358783

 

Aops, https://artofproblemsolving.com/community/c4t48f4h3668514_angle_chasing

 

Erdem Balkan, Geometria Super Top, https://www.facebook.com/groups/830782544358783/?multi_permalinks=2059256738178018%2C2058617761575249¬if_id=1758347506002987¬if_t=group_activity&ref=notif

 

https://artofproblemsolving.com/community/c4t48f4h2130476_isosceles_and_perpendicular_right_isosceles_2016_romanian_nmo_grade_vii_p4

 

Thiago Durado, https://www.facebook.com/photo?fbid=1077295091238115&set=gm.1434936337598221&idorvanity=544207276671136

 

aops, https://artofproblemsolving.com/community/c4t48f4h3635070_atsbsd_wanted_abcd_cyclic_2024_germany_r4_96

 

YouTube channel of Hasan Ata, https://www.youtube.com/watch?v=wUjgygA74ZQ

 

Best Mathematics Problems, Thiago Durado, https://www.facebook.com/photo?fbid=24335162042815456&set=gm.977136487730248&idorvanity=569006668543234

 

F.B. Netai Chandra Bhar, https://www.facebook.com/photo?fbid=24456296070725258&set=gm.1490420385728604&idorvanity=1216680106435968

 

I Love Geometry, Thiago Durado, https://www.facebook.com/photo/?fbid=1058169903150634&set=gm.1484630649640911&idorvanity=1216680106435968

 

FB page of Thiago Durado, https://www.facebook.com/groups/830782544358783/permalink/2028099231293769/

 

FB page of Jafar Nikpour, https://www.facebook.com/photo/?fbid=1563988550925761&set=pcb.1563989067592376

 

aops, https://artofproblemsolving.com/community/c6t48f6h3622666_easy_geometry_in_triangle

 

Geometria Super Top, Nabi Toporan, https://www.facebook.com/photo/?fbid=30563873163227190&set=gm.2019853888784970&idorvanity=830782544358783

 

aops, https://artofproblemsolving.com/community/c6h3617076p35436137

 

FB https://www.facebook.com/photo.php?fbid=10162825605139371&set=p.10162825605139371&type=3

 

Aops, https://artofproblemsolving.com/community/c4t48f4h3616471_find_the_value_of_angle_c

 

Problem, lost source

 

Another solution of https://www.facebook.com/photo?fbid=4695212660554761&set=gm.1282324112279677

 

https://www.facebook.com/photo/?fbid=10162011604082198&set=gm.1458909885546321&idorvanity=1216680106435968

 

FB page of Nelson Tunala, https://www.facebook.com/photo/?fbid=23905833795725106&set=a.373249732743510

 

Fatih Sultan Yildirim Mehmet, I Love Geometry, https://www.facebook.com/photo/?fbid=10164331095994617&set=gm.1456142312489745&idorvanity=1216680106435968

 

I love Geometry, https://www.facebook.com/photo?fbid=24066772916296920&set=gm.1456071139163529&idorvanity=1216680106435968

 

https://www.facebook.com/photo?fbid=7897833440299617&set=a.712949622121404

 

Thiago Durado, https://www.facebook.com/photo?fbid=1023727319928226&set=gm.1433149611369642&idorvanity=1193487768669162

 

FB page of Chris Wildhagen, https://www.facebook.com/photo?fbid=1481372766356568&set=gm.1991861554917537&idorvanity=830782544358783

 

Mathstackexchange, https://math.stackexchange.com/questions/4112110/need-a-pure-geometric-solution-to-a-20-30-130-triangle-question?rq=1

 

FB page of Thiago Durado, https://www.facebook.com/photo/?fbid=1023025149998443&set=a.304452958522336

 

aops, https://artofproblemsolving.com/community/c6t48f6h3599961_prove_that_two_angles_are_equal_on_a_rectangle

 

Triple angle lemma

 

FB page of Nelson Tunala, https://www.facebook.com/photo/?fbid=10031253546943032&set=a.542610499140765

 

Geometria Super Top, https://www.facebook.com/photo?fbid=9331301963636165&set=gm.1985486205555072&idorvanity=830782544358783

 

aops, https://artofproblemsolving.com/community/c6t48f6h3597307_geometry_problem

 

aops, https://artofproblemsolving.com/community/c4t48f4h3596137_difficult_triangle_angle_chasing

 

https://www.facebook.com/photo?fbid=122242400462203033&set=gm.1983140779122948&idorvanity=830782544358783

 

Trazo Geometrico Maldito, Alexsander AC, https://www.facebook.com/photo?fbid=10220811120707581&set=gm.1826856031159813&idorvanity=715291165649644

 

FB, Trazo Geometrico Maldito, https://www.facebook.com/photo/?fbid=1609031989960973&set=a.1172983803565796, problem 231

 

FB page of Hasan Ata, https://www.facebook.com/photo?fbid=8697671933649093&set=a.712949622121404

 

aops, https://artofproblemsolving.com/community/c4t48f4h3579684_a_geometry_problem_to_calculate_the_size_of_an_angle