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等边三角形ABC的边长为2沿平行于BC的线段PQ折起.使平面APQ⊥平面PBCQ.设点A到
等边三角形ABC的边长为2沿平行于BC的线段PQ折起.使平面APQ⊥平面PBCQ.设点A到
发布时间:2021-02-20 14:21:00
等边三角形ABC的边长为2沿平行于BC的线段PQ折起,使平面APQ⊥平面PBCQ,设点A到直线PQ的距离为x,AB的长为d.(Ⅰ)x为何值时,d2取得最小值,最小值是多少;(Ⅱ)若∠BAC=θ,求cosθ的最小值.
网友回答
答案:
分析:
(I)如图(1)为折叠前对照图,图(2)为折叠后的空间图形.利用面面垂直和线面垂直的判定与性质定理和二次函数的单调性即可得出;
(II)在等腰△ADC中,使用余弦定理和利用余弦函数的单调性即可得出.
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