如图,把正方形纸片ABCD沿对角线AC折成直二面角,E,F分别为AD,BC的中点,O是原正方形ABCD的中心,求折纸后
的大小.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2b2557547eecdc826b8282058802d217.png)
更新时间:2021-02-07 16:27:51
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【知识点】 共面直线夹角的向量求法
相似题推荐
解答题-证明题
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适中
(0.65)
名校
【推荐1】在如图所示的试验装置中,两个正方形框架
的边长都是1,且它们所在的平面互相垂直.活动弹子M,N分别在正方形对角线
和
上移动,且
和
的长度保持相等,记
.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/4/12/7465a3be-701c-47f7-9188-87828826c215.png?resizew=153)
(1)求证:
平面
;
(2)当
的长度最小时,求二面角
的余弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6f9f1d8b6eead1dc79af156d6a113431.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/274cf35acb4a1748d15c39d15a9bea7b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db54223bb3fc2fe2497213a4d1f94827.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7785afeeaf274892253d04b4f693b367.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7c57b05fe8f42db9a074224b2a02f78.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/4/12/7465a3be-701c-47f7-9188-87828826c215.png?resizew=153)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7592c4f01c8e06c7ee90df5b9413a9f5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/500df0e782bb081e608f4bc1d576afcf.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411461db15ee8086332c531e086c40c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0912d666aa93db05c94bb8c0368a9790.png)
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解答题-证明题
|
适中
(0.65)
解题方法
【推荐2】如图,设
为正方体,动点
在对角线
上,记
.
(1)证明:
;
(2)当
为钝角时,求
的取值范围.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9fe734023d4e70010a6b2cc3267cb86e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cd445c6377d1ced1f8aa34f5c772b24b.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/11/20/30a69664-4580-45f3-8720-d79612123aaf.png?resizew=150)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4a0dba7306bdaf6e1011c146dea29172.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac3c1375c64dceef45846308a418cf7f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df64046e91b047037f19e4032e3b6de3.png)
您最近一年使用:0次