题目:如图1,在三棱锥V-ABC中,VC⊥底面ABC,AC⊥BC,D是AB的中点,且AC=BC=a,∠VDC=θ(0<θ<(π/2).(Ⅰ)求证:平面VAB上平面VCD;(Ⅱ)当角θ变化时,求直线BC与平面VAB所成的角的取值范围.分析:本题照顾了使用9A,9B两个版本的学生,既能用传统方法解答,也能借助向量论证,体现了面向全体,背景公平的原则.第(Ⅰ)问考查平面与平面 Title: As shown in Fig. 1, in the triangular pyramid V-ABC, VC⊥ bottom surface ABC, AC⊥BC, D is the middle point of AB, and AC=BC=a, ∠VDC=θ (0<θ<(π/2) (I) Verification: Plane VAB plane VCD; (II) When the angle θ changes, find the range of angles formed by the straight line BC and the plane VAB. Analysis: This question takes care of the use of 9A, 9B versions Students can answer both traditional methods and vector arguments, embodying the principle of fairness towards the whole and the background. Section (I) Asking for examination of planes and planes