运用法向量可以使求二面角的方法大大简化,降低解题难度。在实际解题过程中,因为所取法向量方向不定,所得两法向量的余弦值可能为正或为负,那么最终二面角是锐角还是钝角,我们主要依赖于对图形的观察。但在某些特殊情况下,从图形上看并不直观,难以观察出正确结果。本文将通过对一道例题的探讨,用三种方法确定法向量的方向,从而用法向量 The use of normal vectors can greatly simplify the method of finding dihedrals and reduce the difficulty of solving problems. In the process of solving the actual problem, because the cosine of the two normal vectors can be positive or negative because the direction of the normal vector is uncertain, then the final dihedral angle is acute or obtuse, and we rely mainly on the observation of the graph. However, in some special cases, it is not intuitively visible and it is difficult to observe the correct result. This article will explore a case study, using three methods to determine the direction of the normal vector, and thus the use of vector