已知正四面体
,点E、F分别为棱CD、AC的中点,点M为线段EF上的动点,设
,则下列说法不正确的是( )
![](https://img.xkw.com/dksih/QBM/editorImg/2022/12/8/cc09667b-1b2e-419a-b8de-88b8c86553b0.png?resizew=172)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/446983c2905a9a039e04eb6541fc2b2a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7c8e773bffdc3689f89c11c52c68b23a.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/12/8/cc09667b-1b2e-419a-b8de-88b8c86553b0.png?resizew=172)
A.直线DA与直线MB所成角随x的增大而增大 |
B.直线DA与直线MB所成角随x的增大而减小 |
C.直线DM与平面ABD所成角随x的增大而增大 |
D.直线DM与平面ABD所成角随x的增大而减小 |
更新时间:2021-09-08 23:22:02
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【推荐1】已知三棱锥
中,
,面
面
,
,点
为
中点,
与面
所成的角为
,则( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63397cda22cb1fad59cf966dfb588643.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60b4c1ae9c57d51e27bbdb001122d3bd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6d077f6da8b2c00b152d4679aa2ed7f7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/39c7b0e15bfcf4bd7214320bc40f5373.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e0629ce42392a7fe9be21d25c39c3e64.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/79a97bb4dcfab4ec7539bc783d563c49.png)
A.![]() | B.点![]() ![]() ![]() |
C.三棱锥的侧面积为![]() | D.![]() ![]() ![]() |
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【推荐2】在直三棱柱
中,各棱长均为2,
分别为线段
的中点,则( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42d3a82b8e587ee890467835bc4e854c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad056c25c0fdcbcc765eb5cbc6093f2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/da62d9c339d604c5ffafc82fc54e2b17.png)
A.平面![]() ![]() | B.![]() |
C.直线![]() ![]() ![]() | D.该棱柱外接球的表面积为![]() |
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【推荐1】如图,正方体
的棱长为1,E为
的中点.F为
的中点,则( )
![](https://img.xkw.com/dksih/QBM/2021/10/16/2830448772562944/2830578772869120/STEM/f54deb08-c51b-4991-8d29-8c4d0cae7153.png?resizew=232)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b7d857811cbd619f868d951aa7a0ab8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d88bf46ad08f9677c37eed1d0369329.png)
![](https://img.xkw.com/dksih/QBM/2021/10/16/2830448772562944/2830578772869120/STEM/f54deb08-c51b-4991-8d29-8c4d0cae7153.png?resizew=232)
A.![]() | B.直线![]() ![]() |
C.直线EF与平面![]() ![]() | D.点B到平面![]() ![]() |
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【推荐2】如图,菱形ABCD中,AB=2,∠DAB=60°,E是AB的中点,将△ADE沿直线DE翻折至△A1DE的位置后,连接A1C,A1B.若F是A1C的中点,则在翻折过程中,下列说法正确的有( )
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/8/e7686b62-13de-4f90-b24b-6d2f077d62c2.png?resizew=430)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/8/e7686b62-13de-4f90-b24b-6d2f077d62c2.png?resizew=430)
A.异面直线A1E与DC所成的角不断变大 |
B.二面角A1﹣DC﹣E的平面角恒为45° |
C.点F到平面A1EB的距离恒为![]() |
D.当A1在平面EBCD的投影为E点时,直线A1C与平面EBCD所成角最大 |
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