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

 

aops, https://artofproblemsolving.com/community/c4t48f4h3585809_geometry

 

Full solution of https://www.facebook.com/photo/?fbid=1899709203808549&set=a.148394885606665

 Thanking to Alin Cretu, 

Unfinished solution of a problem by Thanos Kalogerakis, https://www.facebook.com/photo?fbid=1899709203808549&set=a.148394885606665

 

FB page of Nelson Tunala, https://www.facebook.com/photo?fbid=9805651689503220&set=gm.945940134183217&idorvanity=569006668543234

 

Thiago Durado, I love Geometry, https://www.facebook.com/photo?fbid=997024679265157&set=gm.1449671353068533&idorvanity=970715314297475

 

Geometria Super Top, Thiago Durado, https://www.facebook.com/photo?fbid=995487406085551&set=gm.1959699281467098&idorvanity=830782544358783

 

Training Geometry Olympiad, Rachid Iksi, https://www.facebook.com/photo?fbid=4196990373868099&set=gm.1351103066150003&idorvanity=293155508611436

 

Aops, https://artofproblemsolving.com/community/c6t48f6h2381913_60o_angle_wanted_equilateral_on_a_square

 

Math For Change, https://www.facebook.com/search/top?q=alpha%20beta%20math

 

Geometria Super Top, Thiago Durado, https://www.facebook.com/photo?fbid=993563456277946&set=a.304452958522336

 

FB page of Nelson Tunala, https://www.facebook.com/photo/?fbid=9759876830747373&set=a.542610499140765

 

Aops, https://artofproblemsolving.com/community/c6t48f6h3575848_problem_3

 

aops, Walther Janous, https://artofproblemsolving.com/community/c6t48f6h2352132_segment_of_projections_is_half_as_sidelength_right_triangle_inscribed_in_right

 

aops, https://artofproblemsolving.com/community/c4t48f4h3566279_incircle_concurrency

 The green marked angles are equal

FB page of Alpha Beta Math, https://www.facebook.com/photo?fbid=122134873910752641&set=a.122096449862752641

 

Nelson Tunala, Geometria Super Top, https://www.facebook.com/photo?fbid=9700785399989850&set=gm.1951914485578911&idorvanity=830782544358783

 

FB Alpha Beta Math, https://www.facebook.com/profile.php?id=61572579235822

 

Math for Change, https://www.facebook.com/profile.php?id=61572579235822

 

FB page of Nelson Tunala, https://www.facebook.com/photo/?fbid=9682593625142361&set=a.542610499140765

 This is my solution found back in Dec. 1989

Problem, Michael de Villiers, https://www.facebook.com/groups/293155508611436

 

Thiago Durado, https://www.facebook.com/photo/?fbid=984384123862546&set=gm.1436606227708379&idorvanity=970715314297475

 

Edson Curahua Ortega, https://www.facebook.com/photo?fbid=379969052114132&set=a.379968675447503

 My solution to this nice lemma, which I call "triple angle lemma".

FB page of Nelson Tunala, from group "Sociedad Geometrica del Peru",

 https://www.facebook.com/photo/?fbid=9572397932828598&set=a.373249732743510,

aops, https://artofproblemsolving.com/community/c4t48f4h3553438_geometry_angle_chasing

 

Nice problem, lost source, again

 Today I saw an old problem on fb geometry sites, with a very nice solution bearing the inconfoundable signature of Master Hasan Ata; attached, my own, which I think you will like! Oops, it's about quadrilateral ABCD, I missed the name!

Aops, https://artofproblemsolving.com/community/c6t48f6h2645441_ratio_of_lengths_in_rightangled_triangle

 

FB page of Nelson Tunala, https://www.facebook.com/photo?fbid=9438291946239198&set=a.542610499140765

 

Nice problem, lost source

 

https://artofproblemsolving.com/community/c4t48f4h3540814_geometry_problem

 

Gogeometry, pb. 1592, https://gogeometry.blogspot.com/2025/02/geometry-problem-1592-semicircle.html

 

Geometria Super Top, Sonu Aarnav, https://www.facebook.com/photo/?fbid=1390909832040285&set=gm.1916474962456197&idorvanity=830782544358783