<Tri-2026-2310>, hint

Suppose line AK cuts BC at P. By Ceva's theorem

(AE/EB )x(BP/PC)x(CF/FA)=1. 

since AE=AF , CF/BE=CP/BP, BE=AB sinB sinA/2 cotB, CF=AC sinC snA/2 cotC

CF/BE= (2R sinB cosC)/(2RsinC cosB).

Let P' be the feet of perpendicular from A then BP'=2R snC cosB, CP'=2RsinB cosC

Hence , CF/BE-CP/BP=CP'/BP', P=P'

<Tri-2026-2310 >, general, bisector

<Singapore MO 2015>



<Tri-2026-2309>, hint


 

<Tri-202-2309>,general, center

<Singapore MO 2013>


 

<Tri-2026-2308>, hint

Suppose AM cuts EF at K'

Since [ABM]=[ACM] ;ABxAM sinBAM=ACxAM sin CAM ; 2RsinC  sinBAM=2RsinB sinCAM

sinBAM/sinCAM=sinB/sinC  Hence FK'/EK'=sinB/sinC

2[DKF]=DFxDK sinB/2=2IF cosB/2 xDK sinB/2=IFx DK sinB

Similarly 2[DKE]=IEx DK sinC. IE=IF ( inradius), [DEK]/[DFK]=EK/FK

Hence EK/FK=sinC/sinB=EK'/FK'. Hence K=K' A,K,M are collinear.