2014·广东湛江·一模
名校
解题方法
1 . 在如图所示的几何体中,四边形
为平行四边形,
,
平面
,
,
,
,
.
![](https://img.xkw.com/dksih/QBM/2014/4/28/1571681095139328/1571681100988416/STEM/d2fd3c26c0c84c68ab2b1ec536cbb2ac.png?resizew=217)
(1)若
是线段
的中点,求证:
平面
;
(2)若
,求二面角
的余弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9ed8f7d3d7043d4b1eb98fc5c4e2fcd3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ed04b01505bbd8a4ac0bc12e46f23bf6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e41d3f7d55fcbaebc4e2450ac63a3dc5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f9c30de91ed42df92510cb64548fe704.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c05f315ab14567942f699983b60d04be.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ed6034301fc4110da89bdb0f46ad82ab.png)
![](https://img.xkw.com/dksih/QBM/2014/4/28/1571681095139328/1571681100988416/STEM/d2fd3c26c0c84c68ab2b1ec536cbb2ac.png?resizew=217)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac047e91852b91af639feec23a9598b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6895bdd0286b8e2704fee9c343d82f57.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/369eb8ad56da7dc1cdb7c43762be4bee.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a9cd88984f891a49ab451a06410a1f0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e4b820c84570da9c38d0a81c22788b76.png)
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2016-12-02更新
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