1 . 如图,在直三棱柱
中,
是
的中点.
![](https://img.xkw.com/dksih/QBM/2016/6/23/1572820601487360/1572820607746048/STEM/d565fa754d5a49cfa56b7e74b1ef9424.png)
(1)求证:
平面
;
(2)若
,
,
,求平面
与平面
所成二面角的正弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/57f47d6a88e962cd790d2f159c021ec1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://img.xkw.com/dksih/QBM/2016/6/23/1572820601487360/1572820607746048/STEM/d565fa754d5a49cfa56b7e74b1ef9424.png)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/896e293411e2fd0da215ff20781cb36a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4ba9e20d667d04bf3ee7f55cc795ce01.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e199a5d02bfb5b869221e61d31969bea.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/883fc5e3faf39829d60804b59deb1730.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/92535536bd3c2761724fd058427f95a8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4ba9e20d667d04bf3ee7f55cc795ce01.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e367b683581c7cbe018078168f69efc5.png)
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2 . 如图,在直三棱柱
中,
分别是
的中点.
![](https://img.xkw.com/dksih/QBM/2016/6/23/1572819806568448/1572819812835328/STEM/8faf1f84db274d4280e47d7c5e35dad1.png)
(1)求证:
平面
;
(2)若
,试在
上找一点
,使
平面
,并证明你的结论.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/57f47d6a88e962cd790d2f159c021ec1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/80bbe13f5c674ba211bc31948cc91151.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/34ec28d9a001761cef6bb3018aa7323c.png)
![](https://img.xkw.com/dksih/QBM/2016/6/23/1572819806568448/1572819812835328/STEM/8faf1f84db274d4280e47d7c5e35dad1.png)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/edcf19a7f0dd0cdf59516ae585025110.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d41adffdf0ce71e5e3fa9b00b418cfa1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e0a851907ada2ac2c3c4880a6736d28a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/82fbae62ef53e398a0e7276c97e7b888.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/14eec658f69c267a70c1e8f9b744e282.png)
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3 . 三棱锥
中,
、
分别是三角形
和三角形
的外心,则下列判断一定正确的是
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/22ea34a4604f4402acf9caa4dec130b3.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/953a4ec30a1b47f09120527aad00b964.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/06b356fee1764f79aca39fb9ffa7ff86.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/346d4c09810940528a06739b97c1a62e.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/c9e96b7066904c269feb79c31e56d602.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/53ec8162465641f2b54da167c3d2a88b.png)
![](https://img.xkw.com/dksih/QBM/2016/5/31/1572673995808768/1572674001477632/STEM/22ea34a4604f4402acf9caa4dec130b3.png)
A.![]() |
B.当![]() ![]() ![]() |
C.当且仅当![]() ![]() ![]() |
D.![]() |
您最近一年使用:0次