平面的交线具有两个平面的某些共性,因而在解题中有如下妙用: 一、借助“平面交线”证明点共线例1 如图1,多面体是由底面为ABCD的平行六面体被截面AEFG所截, 若BD与EG交于H,CD与FG交于I,CB与 FE交于J,求证:H,I,A,J四点在一条直 The intersection line of the plane has some commonalities of the two planes, and thus has the following magical effect in solving the problem: 1. Proof of the collinearity of the point by “plane intersection” Example 1 As shown in Fig. 1, the polyhedron is a parallelepiped with an ABCD bottom surface. Section AEFG is cut, if BD and EG intersect at H, CD and FG intersect at I, CB and FE at J, verify: H, I, A, J are in a straight line