立体几何中的求二面角大小问题,是高考重点考查内容,法向量法是求二面角大小的一种主要方法.我们知道:二面角大小与其两个平面的法向量的夹角相等或互补.但到底是相等还是互补,教学中很多师生采用直观判断,参考资料涉及此问题也回避不谈.文[1]给出了一种很好的判定方法,本文给出 Stereo geometry to find the dihedral angle of the size of the examination is the focus of the entrance examination, the normal vector method is to find a dihedral angle size of a main method.We know that: the dihedral angle and its two planes normal vector angle Or complementary, but in the end is equal or complementary, teaching a lot of teachers and students to use intuitive judgments, references to this issue also to avoid talking about article [1] gives a good decision method, this article gives