题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121134-43917.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121134-80489.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-28899.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-14023.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-12485.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-17839.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-12576.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-20209.png)
(1)证明:
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-33749.png)
(2)求二面角
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-48316.png)
(3)求点
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-43186.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-64948.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-33749.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-48316.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-14574.png)
(3)点
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-43186.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-64948.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-44888.png)
解析
解:(1)证明:取线段
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-26978.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-95078.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121138-50765.png)
因为
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121138-28218.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121138-14829.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121138-26782.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121138-50357.png)
因为平面
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-28899.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-14023.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121139-26045.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121139-78848.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121139-93249.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-14023.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121139-62727.png)
建立如图所示空间直角坐标系,则
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121140-89485.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121140-82185.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121140-31735.png)
因为
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121140-31565.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121140-41315.png)
即
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121141-66312.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121141-65482.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121135-14023.png)
由(1)得:
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121141-21804.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121141-85212.png)
设
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121142-69506.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-64948.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121142-24289.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121142-93052.png)
取
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121142-72082.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121142-34498.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121143-26802.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121143-20399.png)
由图可知:二面角
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-48316.png)
所以二面角
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-48316.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-14574.png)
(3)由(1)(2)可得:
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121143-67685.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121143-81751.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-64948.png)
所以,点
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121136-43186.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121137-64948.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121144-24973.png)
核心考点
举一反三
如图,在四棱锥
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-83480.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-48414.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-39751.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-58908.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-64910.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-50749.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-22671.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-63614.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-57371.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-10441.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-23497.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-45551.png)
(Ⅰ)证明:
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-53889.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-55737.png)
(Ⅱ)设三棱锥
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-86944.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121111-83480.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-25660.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-60077.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121112-53671.png)
A.![]() | B.![]() | C.8![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121054-35239.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191021/20191021121054-54201.jpg)
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