∵ ∠BAC=90°
∴∠CAE+∠BAD=90°
∵BD⊥AE
∴∠ABD+∠BAD=90°
∴∠ABD=∠CAE
∵AB=AC ∠ADB=∠CEA=90°
∴△ABD ≌△CAE
∴AD=CE BD=AE
∵DE=AE+AD
∴DE=BD+CE