Mi Prepa, https://www.facebook.com/photo?fbid=1427344626075511&set=a.575642501245732

 

Mi Prepa, https://www.facebook.com/photo?fbid=1427344626075511&set=a.575642501245732

In the interior of triangle ABC having  there is a point D having . Find .

Proof:

Take E reflection of B across CD, it lies onto CA and D is the circumcenter of ; according to lemma proved at https://stanfulger.blogspot.com/2026/05/problem-lost-source.html,
AE = AD. With  we infer .

Problem, lost source

 

Geometria Super Top, Alexander James Sirens, https://www.facebook.com/photo?fbid=3252905348223065&set=gm.2258144711622552&idorvanity=830782544358783

 

Geometria Super Top, Selcuk Bicer, https://www.facebook.com/photo?fbid=27762870359969042&set=gm.2257061028397587&idorvanity=830782544358783

 

Geometria Super Top, Mathci Jafar, https://www.facebook.com/photo?fbid=122106150452693674&set=gm.2253371212099902&idorvanity=830782544358783

 

Gogeometry, Antonio Gutierrez, https://gogeometry.blogspot.com/2023/03/geometry-problem-1523-discover-how-to.html

 

Aops, Erik Lim, https://artofproblemsolving.com/community/c6t48f6h3821925_angle_aob_in_a_triangle_with_a_bisector_and_ratio_point