众所周知 ,在平面几何中 ,如果线段ＡＢ的中点在直线ｌ上 ,那么Ａ、Ｂ两点到直线ｌ的距离相等 .在立体几何中有同样类似的结论 :如果Ａ、Ｂ两点在平面α的异侧 ,且线段ＡＢ的中点在平面α上 ,那么Ａ、Ｂ两点到平面α的距离相等 .证明　如图 1 ,过Ａ、Ｂ两点分别作平面α的垂线 As we all know, in plane geometry, if the midpoint of the line segment AB is on the line l, then the distance from point A to line B is equal to the line l. There are similar conclusions in the three-dimensional geometry: if two points A and B are in the plane α The other side, and the middle point of the line segment AB is on the plane α, then the distances from the two points A and B to the plane α are equal. Prove that in Figure 1, the two points A and B are perpendicular to the plane α.