在历年的立体几何高考题中,求二面角的大小是必考的内容,二面角的求法理所当然成为高三复习的重点,但也没有必要把每一种方法每一种情况都选配一个例题来讲解或练习,这样又费时重点又分散也不利于学生掌握.下面笔者仅选了一例,不但复习总结了二面角的五种求法,还突出了无棱二面 In the three-dimensional geometry entrance examination questions in the calendar year, the size of the dihedral angle is the content of the exam. The dilemma of the dilemma is of course the focus of the third-year review, but it is not necessary to match each method with each case. Examples to explain or practice, this time-consuming and scattered focus is also not conducive to student mastering. The following author only selected one example, not only reviewed the five methods of dihedral angle, but also highlights the two sides