题目内容
如图,直四棱柱
中,底面
是直角梯形,
,
,
.
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(1)求证:
是二面角
的平面角;
(2)在
上是否存一点
,使得
与平面
与平面
都平行?证明你的结论.
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(1)求证:
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(2)在
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(1)见解析(2) 存在点
,
为
的中点,证明见解析
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试题分析:(1) 直棱柱
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又
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∴
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∴
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(2)存在点
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由
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又∵
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∴
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又
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同理,
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点评:证明一个问题,首先要分析需要什么条件,需要用到什么定理,然后把需要用到的定理的条件一一列举出来,缺一不可,数学证明题必须严谨.
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