如图所示,四边形ABCD中,AD垂直DC,BC垂直AB,AE平分∠BAD,CF平分∠DAB,AE交CD于E,CF交AB于

∵AD⊥DC,BC⊥AB,AE平分∠BAD,CF平分∠DAB
∴∠EAB+∠FCB=90°
∠CFB+∠FCB=90°
∴∠EAB=∠CFB
∴AE//CF