(2)DE=BD+CE.
∵∠BAC=90°,∴∠BAD+∠CAE=90°,
∵CE⊥AE,∴∠ACE+∠CAE=90°,
∴∠ACE=∠BAD;
又∵BD⊥AE,CE⊥AE且AB=AC,
∴△ABD≌△CAE(AAS),
∴BD=AE,AD=CE;
∵DE=AE+AD,
∴DE=BD+CE
(2)DE=BD+CE.
∵∠BAC=90°,∴∠BAD+∠CAE=90°,
∵CE⊥AE,∴∠ACE+∠CAE=90°,
∴∠ACE=∠BAD;
又∵BD⊥AE,CE⊥AE且AB=AC,
∴△ABD≌△CAE(AAS),
∴BD=AE,AD=CE;
∵DE=AE+AD,
∴DE=BD+CE