辅助线：延长CB到G,使BG=DF
∵正方形ABCD,AB=AD,AB⊥BC,AD⊥DC
∴△ABG全等于△ADF
∴∠GAB=∠FAD,∠AGB=∠AFD
∵AF平分角EAD
∴∠GAB=∠FAE
∵AB‖CD
∴∠AFD=∠FAB
∴∠GAB =∠FAB=∠GAE
∴△AEG为等腰△,AE=EG=BE+BG=BE+DF