一、两个平面的位置关系 我们观察放在桌面α上的长方体,它的各相对的面都没有公共点,我们称这样的两个面为平行平面;它的相邻两个面都相交于一条直线,我们称这样的两个面为相交平面;长方体的下底面与桌面α完全重合。事实上,如果两个平面有不共线的三个公共点时,它们就完全重合。 First, the relationship between the two planes We observe the rectangular parallelepiped on the desktop alpha, its opposite faces have no common point, we call such two planes as parallel planes; its two adjacent surfaces intersect at In a straight line, we call such two planes as intersecting planes; the bottom surface of the cuboid completely coincides with the desktop α. In fact, if two planes have three common points that are not collinear, they completely coincide.