两平面立体相交Two plane solids intersect

     两平面体的相贯线是空间闭合折线或平面多边形 。此空间折线或平面多边形的各直线段是两平面体上相应平面的交线；折线的顶点是一个立体的棱线或底边与另一立体表面的交点，称为折点。

    求两平面体相贯线的方法有两种：

     1. 求出一平面体上各平面与另一立体的截交线，组合起来，得到相贯线；

     2. 求出两个平面体上所有棱线及底边与另一立体表面的交点（贯穿点），按一定规则连线得到相贯线。

    为了避免作图的盲目性，在解题前应先分析两立体上有哪些平面、哪些棱线及底边参与相贯。

    The intersecting lines of two plane bodies are space closed polygons or plane polygons.The straight segments of the spatial polyline or plane polygon are the intersecting lines of the corresponding planes on the two plane bodies.The vertex of a polyline is the point at which the edge or bottom of a solid intersects the surface of another solid.

     There are two ways to find the intersecting line of two planes:

     1. Find out the intersecting lines between each plane on a plane body and another solid body, combine them, and get the intersecting line;

     2. Find out the intersection point (through point) of all prisms and bottom edges on the two plane bodies and the other solid surface, and get the intersecting line according to certain rules.

     In order to avoid the blindness of drawing, we should first analyze which planes, which edges and bottom edges are intersecting on two solids before solving the problem.

     举例，求作相贯线：