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求二面角的平面角的大小是高考考试的重点,常见的方法如定义法,三垂线法,补棱法,射影面积法,向量法等.高考中常用的方法是定义法,三垂线法和向量法.一.两道习题习题1、如图(1),P是二面角α-AB-β的棱AB上一点,分别在α,β上引射线PM,PN,截PM=PN,如果∠BPM=∠BPN=45°,∠MPN=60°,则二面角α-AB-β的大小是___________.(1)(2)习题2、如图(2),在四面体ABCD中,ΔABD,ΔACD,ΔBCD,ΔABC都全等,且AB=AC=3,BC=2,求以BC为棱、
Seeking the dihedral angle of the plane angle is the focus of college entrance examination, common methods such as the definition of law, the three vertical line method, fill edge method, projective area method, vector method, etc. Commonly used in college entrance examination is the definition of law, (1), P is the point on the edge AB of the dihedral angle α-AB-β, and leads the lines PM and PN respectively on α and β, and cuts off the PM = PN, if ∠BPM = ∠BPN = 45 °, ∠MPN = 60 °, the size of dihedral angle α-AB-β is ___________. (2) Exercise 2, In the tetrahedron ABCD, ΔABD, ΔACD, ΔBCD and ΔABC are congruent, and AB = AC = 3 and BC = 2,