解题方法
1 . 阅读下面题目及其证明过程,在
处填写适当的内容.
已知三棱柱
,
平面
,
,
分别为
的中点.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/3/27/daabe3a8-f5d5-4b94-9577-eeb61c3f5b0f.png?resizew=135)
(1)求证:
∥平面
;
(2)求证:
⊥
.
解答:(1)证明: 在
中,
因为
分别为
的中点,
所以 ① .
因为
平面
,
平面
,
所以
∥平面
.
(2)证明:因为
平面
,
平面
,
所以 ② .
因为
,
所以
.
又因为
,
所以 ③ .
因为
平面
,
所以
.
上述证明过程中,第(1)问的证明思路是先证“线线平行”,再证“线面平行”; 第(2)问的证明思路是先证 ④ ,再证 ⑤ ,最后证“线线垂直”.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/80d5d02301554aad6cc89452c83f0862.png)
已知三棱柱
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42d3a82b8e587ee890467835bc4e854c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5845ccc0d735dc14c92a8926d9b1def6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9c06154cae3bf7a8ce5a1e97a7380875.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad056c25c0fdcbcc765eb5cbc6093f2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/62d77afb7d8280995886ff690e7a6c9a.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/3/27/daabe3a8-f5d5-4b94-9577-eeb61c3f5b0f.png?resizew=135)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
(2)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3ee8456443402a25b1e25d35ff7e1c98.png)
解答:(1)证明: 在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8f9e1e0d29bc4bdf0c6d38ca4db43343.png)
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad056c25c0fdcbcc765eb5cbc6093f2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/62d77afb7d8280995886ff690e7a6c9a.png)
所以 ① .
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/871502ee0c5d1414cfe81e8409b62d76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f196748dc6a0d0bd9e9e4dd30ac4ed0e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
(2)证明:因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5845ccc0d735dc14c92a8926d9b1def6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be509ef5101aae24609ff9941cb246fc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
所以 ② .
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9c06154cae3bf7a8ce5a1e97a7380875.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/36c4559d27e3905980d1a4f1856f07de.png)
又因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e5d970e34169fb0de8a3f10e4c6ae40d.png)
所以 ③ .
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f6cb3896ef1afc6a56a5aa0243022e0d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6ac61c24f99a4e466f1e2ea011893866.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba985fb50a9078a839b66bf1d1eadea9.png)
上述证明过程中,第(1)问的证明思路是先证“线线平行”,再证“线面平行”; 第(2)问的证明思路是先证 ④ ,再证 ⑤ ,最后证“线线垂直”.
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