求二面角的大小是立体几何中的重点和难点,也是多年来高考的考查热点.利用三垂线定理(或逆定理)求二面角的大小是我们常用的基本方法,也是重要的方法.当然,我们在掌握基本方法(三垂线法)的同时还应该去研究二面角的其他求法.本文就一道高考题谈谈二面角的求法,供参考.题目(2006 Finding the size of the dihedral angle is the key and difficult point in the three-dimensional geometry, and it is also a hot spot for the college entrance examination over the years. Using the tri-perpendicular theorem (or the inverse theorem) to find the size of the dihedral angle is a commonly used basic method, and it is also an important method. Of course, we should also study the other methods of dihedral angle while mastering the basic method (three vertical lines). This article talks about the method of dihedral angle for a college entrance examination question, for reference. Topic (2006