利用平面的法向量可以方便地求出二面角平面角的大小,由于两法向量的夹角未必就是二面角的平面角的大小,许多杂志上都介绍了直接从图形上观察两法向量的方向,来确定两法向量的夹角是否为两平面的夹角.这种方法虽然简单,但由于空间任意两个向量都是共面的,要从图形上直接判定他们的方向,需要很强的空间想象能力,好多学生是达不到这种境界的.在最后的复习中,我利用下面的 The use of planar normal vectors can be easily found in the size of the dihedral plane angle, because the included angle of the two normal vectors is not necessarily the size of the plane angle of the dihedral angle, many magazines have introduced direct observation from the graphical two normal vectors The direction to determine whether the angle between the two normal vectors is the angle between the two planes. This method is simple, but since any two vectors in space are coplanar, it is necessary to determine their direction directly from the graph. With strong spatial imagination, many students are unable to reach this realm. In the final review, I use the following