题目
题型:不详难度:来源:
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(Ⅰ)求证:
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(Ⅲ)当
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答案
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∵
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∴
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∴
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又∵
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∴斜线
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∴由三垂线定理,得
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故,
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(Ⅱ)以
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设
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∴
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同理可求:
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∴
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故,二面角
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(Ⅲ)显然
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因
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设
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由题意,得
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即
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故,当点
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解析
核心考点
试题【如图,四棱锥中,底面是平行四边形,底面(Ⅰ)求证:;(Ⅱ)若,求二面角的余弦值;(Ⅲ)当时,在线段上是否存在一点使二面角为,若存在,试确定点的位置;若不存在,请】;主要考察你对空间几何体的结构特征等知识点的理解。[详细]
举一反三
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① 若
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A.2 | B.![]() | C.3 | D.![]() |
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(1) 证明:
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(2) 证明:
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(3) 求四棱锥
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(1)若
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(3
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其中正确命题的个数是
A.0 | B.1 | C.2 | D.3 |
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