∵AE=AD
∴∠ADE=∠AED
∵ABCD是矩形,DF⊥AE
∴∠ADE+∠CDE=∠FED+∠CDE=∠FED+∠FDE=90°
∴∠CDE=∠FDE
在RtΔDFE与RtΔDCE中,∠CDE=∠FDE,DE为公共边
∴RtΔDFE≌RtΔDCE
∴CE=EF