二面角是立体几何的重要内容 ,是高考命题的热点 ,也是教学中的难点 .下面以一道高考题为例谈谈求二面角的常用方法 .( 2 0 0 1全国高考题 )如图 1,在底面是直角梯形的四棱锥S -ABCD中 ,∠ABC =90°,SA ⊥面ABCD ,SA =AB=BC =1,AD =12 .( 1)求四棱锥S -ABCD的体积 ;( 2 )求面SC Dihedral angle is an important content of the three-dimensional geometry, is the hot spot of the college entrance examination proposition, but also a difficult point in teaching. The following to a college entrance examination question as an example to talk about the common method of dihedral angle. (2001 national college entrance examination questions) Figure 1, In the quadrangular pyramid S-ABCD with a right-angle trapezoid on the bottom, ∠ ABC = 90°, SA ⊥ ABCD, SA = AB = BC =1, AD = 12 (1) Find the quadratic pyramid S - ABCD volume; (2) Surface Search SC