考生在求二面角的大小时,常用定义法与向量法,很少用等积法.然而,等积法不仅是一种求二面角大小的通法,有时甚至胜于定义法与向量法.例题如图1,在四棱柱ABCDA_1B_1C_1D_1中,侧棱A_1A⊥底面ABCD,AB∥DC,AB⊥AD,AD=CD=1,AA_1=AB=2,E为棱AA_1的中点,求二面角B_1-CE-C_1的正弦值.等积法的基本思路过点C_1作C_1O⊥平面B_1CE,交平面B_1CE于点O,作C_1F⊥CE,交CE于点 Candidates seeking the size of the dihedral angle, commonly used in the definition of law and the vector method, seldom use the equal product method.However, the equal product method is not only a method of seeking dihedral angle of the law, and sometimes even better than the definition of law and vector Example. As shown in Figure 1, in the quadrangular prism ABCDA_1B_1C_1D_1, ABCD, AB∥DC, AB⊥AD, AD = CD = 1, AA_1 = AB = 2, A is the midpoint of the edge AA_1, Angle of face B_1-CE-C_1.The basic idea of ​​equal-volume method is to point C_1 to C_1O⊥ plane B_1CE and to intersect plane B_1CE at point O, to make C_1F⊥CE, to point CE at point