∵四边形ABCD是正方形
∴AB=AD,∠BAD=∠D=90°
∵AE=DF
∴⊿ABE≌⊿DAF
∴∠AFD=∠AEB
∵∠DAF+∠AFD=90°
∴∠DAF+∠AEB=90°
∴∠AGE=90°
∴BE⊥AF