Just prove △ BDE △ FDC.

AD is the bisector of triangle ABC ∠BAD=∠FAD.

∠ Abd =∠ Fad = 90 AD = AD。

∴△BAD≌△FAD ∴BD=FD

∠ EBD =∠ CFD = 90 be = CF。

∴△EBD≌△CFD

∴DE=CD

Proof: Connect autofocus.

∵BD⊥AN,CE⊥AM

∴∠BDC=∠CEB=90,∠ADF=∠AEF=90

∠∠BFE =∠CFD，CD=BE

∴△BFE≌△CFD

∴DF=EF

AF = AF

∴△ADF≌△AEF (HL)

∴∠DAF=∠EAF

Point f is on the bisector of point a.