Thiago Durado, I Love Geometry, https://www.facebook.com/photo?fbid=1283481923952763&set=gm.1722055809231726&idorvanity=1216680106435968

 

Thiago Durado, Geometria Super Top https://www.facebook.com/photo?fbid=1282033827430906&set=gm.2271128366990853&idorvanity=830782544358783

 

Thiago Durado, I Love Geometry https://www.facebook.com/photo?fbid=26908591615449294&set=gm.972472982159415&idorvanity=195960136477374

 

Selçuk Biçer, Geometria Super Top https://www.facebook.com/photo/?fbid=27989747883947954&set=gm.2272984176805272&idorvanity=830782544358783

 

Selçuk Biçer, Geometria Super Top https://www.facebook.com/photo?fbid=27986904327565643&set=gm.2272807920156231&idorvanity=830782544358783

 

Trazos Auxiliares en Geometria, Nelson Tunala, https://www.facebook.com/photo?fbid=26869205252721264&set=gm.970115739061806&idorvanity=195960136477374

 

Geometria Super Top, Fatih Eymen Hallaç, https://www.facebook.com/photo?fbid=10163777728503190&set=gm.2270719707031719&idorvanity=830782544358783

 For explanation and proof of triple angle lemma you may scroll my blog!

aops, https://artofproblemsolving.com/community/c4t48f4h2035282_dab90oadc___bam____adb___cam_kharkiv_city_x_2017_ukr

 

Nelson Tunala, Trazos Auxiliares en Geometria, https://www.facebook.com/photo?fbid=26831171749857948&set=gm.967353269338053&idorvanity=195960136477374

 

Alexander James Sirens, Geometria Super Top, https://www.facebook.com/photo?fbid=3264273037086296&set=gm.2267871483983208&idorvanity=830782544358783

 

John Tsilai, Math Lovers, https://www.facebook.com/photo?fbid=3195025937372122&set=gm.2221539305261075&idorvanity=319322575482767

 

Geometria Super Top, Alexander James Sirens, https://www.facebook.com/photo?fbid=3259799400866993&set=gm.2264051727698517&idorvanity=830782544358783

 

Nelson Tunala, Pre Geometria Trigonometria https://www.facebook.com/photo?fbid=26334807416161053&set=gm.4310259995883206&idorvanity=1660116210897611

 

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

 

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