证明：∵∠BAC=90°∴∠ABE+∠AEF=90°
∵∠ADB=90°,∴∠DBE+∠DFB=90°
∵∠ABE=DBE∴∠AEF=∠DFB
∵∠DFB=∠AFE∴∠AEF=∠AFE
∴AE=AF