如图,平面AA1B1B上.把⊿ABE绕O﹙AA1B1B的中心﹚顺时针旋转90º,到达⊿A1AG,
∴AG=BE=AB/2G是AB中点.∴A1D1FG是矩形D1F∥=A1G
A1G⊥AE﹙∵A1G由AE旋转90º得来.﹚,∴ D1F⊥AE.