用平面的法向量求二面角是一种通法,本文谈用向量法求二面角的另一通法:在具体立体几何题中二面角以图1的形式给出,即二面角的两个面是以三角形的形式出现的,分别作高AE、DF,如图2,则向量(?)与(?)(或(?)与(?))的夹角等于二面角A-BC-D的平面角. Diagonal angle is a general method using the planar normal vector. This article talks about the other way of using the vector method to find the dihedral angle: In the specific three-dimensional geometry problem, the dihedral angle is given in the form of Figure 1, ie dihedral angle The two faces are in the form of triangles, respectively, for high AE, DF, as shown in Figure 2, the vector (?) And (?) (or (?) And (?)) angle equal to the dihedral angle A - Plane angle of BC-D.