证明：AD⊥BC,AB⊥AC.∠B+∠BAD=90°∠DAC+∠BAD=90°∠B=∠DAC
∠AEF=∠DAC+∠ACE,∠AFE=∠B+∠FCB ∠ACE=1/2∠ACB=∠FCB
∴∠AEF=∠AFE.AF=AE