<Tri-2026-2380>, hint

Suppose line DI  cuts incircle at H and AG at K respectively,

and AI cut EF at M, midpoint of EF and so  <AMG=90 

Suppose a circle AGM (AG is diameter) cut incircle at J. <AJG=90=<AJD

Suppose JA cut incircle  at H'. Since <H'JD=90, H' lie on line DI, H' lie on incircle, and H'(=H) is the intersection of AJ and DK, which is orthocenter of triangle ADG

<Tri-2026-2380>, general, center

<Spain MO 2026>


 

 <Tri-2026-2379>, hint


OM=R cosA

AH= AB cosA/sinC=2R sinc cosA/sinC=2R cosA

<Tri-2026-2379>, general, center

<Spain MO 2025>


 

<Qua-2026-832>, hint