证明:在△ABD和△ACE中
AB=AC,BD=CE,∠BAD=∠CAE=90
所以△ABD≌△ACE.∠DBA=∠ECA,∠ADB=∠AEC
∵∠ECA+∠AEC=90∴∠ECA+∠ADB=90
∠ADB=∠FDC
∴∠FDC+∠ECA=90
∴∠DFC=90
BF⊥CE
证明:在△ABD和△ACE中
AB=AC,BD=CE,∠BAD=∠CAE=90
所以△ABD≌△ACE.∠DBA=∠ECA,∠ADB=∠AEC
∵∠ECA+∠AEC=90∴∠ECA+∠ADB=90
∠ADB=∠FDC
∴∠FDC+∠ECA=90
∴∠DFC=90
BF⊥CE