解:∵∠BAC=90°
∴∠BAD+∠CAE=90°
∵CE⊥DE
∴∠ACE+∠CAE=90°
∠BAD=∠ACE
△DBA△EAC
∠ADB=90°=∠CEA
∠BAD=∠ACE
AB=AC
∴△DBA≌△EAC
DB=AEAD=CE
故DE=AD+AE=BD+CE
解:∵∠BAC=90°
∴∠BAD+∠CAE=90°
∵CE⊥DE
∴∠ACE+∠CAE=90°
∠BAD=∠ACE
△DBA△EAC
∠ADB=90°=∠CEA
∠BAD=∠ACE
AB=AC
∴△DBA≌△EAC
DB=AEAD=CE
故DE=AD+AE=BD+CE