解题方法
1 . 在直三棱柱
中,
,D、E、F分别为棱
和
的中点.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/1/13d77b45-67fb-41ea-9936-2df546a427f1.png?resizew=124)
(1)求证:
平面
;
(2)求证:
;
(3)若
,求三棱锥
的体积.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/71f2185273bf04c11118c7954f7ec822.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3788d69acba900ae9e013ef0a23bb347.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b0d6885901907652b1653be2cef5f665.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20ecac2dad4cffdd971fd23deacff3fc.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/1/13d77b45-67fb-41ea-9936-2df546a427f1.png?resizew=124)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b78172568aac9805d2ea2d5f742bf80c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b0bc51695e51aa8cd2f97d220c8f5340.png)
(2)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6a7a3dc3f3a02f4400e22dec2f2fee23.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5034b24ff73d35c3f34e5c45daa0624d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05925f665156215b1e031ea6c190616a.png)
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解题方法
2 . 已知球O的直径为
,圆柱
的底面直径和高均为
,设球O的表面积为
,圆柱
的表面积为
,则
的值为_____ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e7f30167e1135806fe9de641870b1e6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e65ac334119ccd6204402a7aba29a55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e7f30167e1135806fe9de641870b1e6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e097c8d4c948de063796bd19f85b3a9a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e65ac334119ccd6204402a7aba29a55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e0bd63f55069a3bc870915010b39225.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/235f0a6fb218d28383e6f27f2df1f50f.png)
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3 . 已知正方体
,设直线
为a,直线
为b,P是棱
的中点,直线l经过点P.则( )
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/30/3ff7b252-669e-4831-ba12-094a22f43679.png?resizew=140)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/394c5d2f55221975503be8aa18022480.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d88bf46ad08f9677c37eed1d0369329.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/30/3ff7b252-669e-4831-ba12-094a22f43679.png?resizew=140)
A.存在无穷多条直线l与a、b都相交 |
B.有且只有一条直线l与a、b都垂直 |
C.若![]() ![]() |
D.若![]() ![]() |
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