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解题方法
1 . 一个长方体的平面展开图及该长方体的直观图的示意图如图所示.
![](https://img.xkw.com/dksih/QBM/2021/12/19/2875651149111296/2878281717874688/STEM/06ec41e4-05e1-4a23-94df-6aca15af764f.png?resizew=363)
(1)请将字母F,G,H标记在长方体相应的顶点处(不需说明理由):
(2)若
且有下面两个条件:①
;②
,请选择其中一个条件,使得DF⊥平面
,并证明你的结论.
![](https://img.xkw.com/dksih/QBM/2021/12/19/2875651149111296/2878281717874688/STEM/06ec41e4-05e1-4a23-94df-6aca15af764f.png?resizew=363)
(1)请将字母F,G,H标记在长方体相应的顶点处(不需说明理由):
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/645c2acbf5a03068cba4d6dff6563976.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e4280be91682e5d8a0d0704190319bb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/faffe3765c15f53305516895aa595a9b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73cc4309dcef077fbcf60099f47b7b37.png)
您最近一年使用:0次
2021-12-22更新
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172次组卷
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2卷引用:广东省佛山市顺德区乐从中学2020-2021学年高二上学期期中检测数学试题
2014·吉林·一模
2 . 一个多面体的直观图及三视图如图所示,其中
分别是
的中点,
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/30/478004d6-0050-48ca-9182-b1b1824dddcf.png?resizew=172)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/30/cbb855ed-264b-41ad-82c0-f848f0f70138.png?resizew=174)
(1)求证:
平面
;
(2)求二面角
的余弦值;
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7789a500686c7a73770404ead6af0590.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/31e4c8af36ed081c96928dc7d8d9012e.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/30/478004d6-0050-48ca-9182-b1b1824dddcf.png?resizew=172)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/30/cbb855ed-264b-41ad-82c0-f848f0f70138.png?resizew=174)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/edcf19a7f0dd0cdf59516ae585025110.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b32c05247f6998d7a70d31d13be4148c.png)
(2)求二面角
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f3fb82553d568ea8aae9d0dd89ae1ca2.png)
您最近一年使用:0次