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