在正三棱柱
中,
为边
的中点.
(1)证明:
平面
.
(2)当
取何值时,
?
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42d3a82b8e587ee890467835bc4e854c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be0c0d0497f5d3f317504d59cc19a4c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6bf9628142422a4884bd59538da6d312.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f6df10d0b03d6f6e640d9c5f3695a4e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6fa8345302e8036af33d4598282144d7.png)
2013高三·天津·竞赛 查看更多[1]
(已下线)2013年全国高中数学联赛天津赛区预赛试题
更新时间:2018-12-14 22:52:30
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解答题-问答题
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适中
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【推荐1】如图,在四棱锥EABCD中,AB∥CD,∠ABC=90°,CD=2AB=2CE=4,点F为棱DE的中点.证明:AF∥平面BCE.
![](https://img.xkw.com/dksih/QBM/2021/9/5/2801701025054720/2809529160269824/STEM/650cdc2b1bc24771a2a73e5a359286ab.png?resizew=228)
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解题方法
【推荐2】如图,在四棱柱ABCD﹣A1B1C1D1中,底面四边形ABCD是矩形,平面DCC1D1⊥平面ABCD.AD=3,CD=DD1=5,∠D1DC=120°,M,N分别是线段AD1,BD的中点.
![](https://img.xkw.com/dksih/QBM/2020/3/4/2412271471992832/2412893459161088/STEM/06170cec-e420-4967-9eca-f56448042182.png)
(1)求证:MN//平面DCC1D1;
(2)求证:MN⊥平面ADC1;
(3)求三棱锥D1﹣ADC1的体积.
![](https://img.xkw.com/dksih/QBM/2020/3/4/2412271471992832/2412893459161088/STEM/06170cec-e420-4967-9eca-f56448042182.png)
(1)求证:MN//平面DCC1D1;
(2)求证:MN⊥平面ADC1;
(3)求三棱锥D1﹣ADC1的体积.
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【推荐1】如图,多面体
是将一个平行六面体
截去三棱锥
后剩下的几何体,点
为三角形
的重心.四边形
是边长为
的正方形,且
,
.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/2/17/86500fa7-17b5-4a62-9711-6b89ad88c86d.png?resizew=167)
(1)求证:
;
(2)求线段
的长;
(3)求异面直线
与
所成角的余弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9164d4bc2ff3ae9d739f7056bfe4d6df.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/99516e53f1ff2599ed3296963d2a51d5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e86eec8526479272d15bb3b171a46de0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bdaa19de263700a15fcf213d64a8cd57.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/92535536bd3c2761724fd058427f95a8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/826693d8d44b581f7d90f01c9efdc2fb.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/2/17/86500fa7-17b5-4a62-9711-6b89ad88c86d.png?resizew=167)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e5ea309886e947ea7cb4b81716206fd.png)
(2)求线段
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
(3)求异面直线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d7f6f93171329d508d491143b9d71f7b.png)
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【推荐2】空间中,两两互相垂直且有公共原点的三条数轴构成直角坐标系.如果坐标系中有两条坐标轴不垂直,那么这样的坐标系称为“斜坐标系”.现有一种空间斜坐标系,它任意两条数轴的夹角均为
,我们将这种坐标系称为“斜
坐标系”.我们类比空间直角坐标系,定义“空间斜
坐标系”下向量的斜
坐标:
分别为“斜
坐标系”下三条数轴(
轴,
轴,
轴)正方向上的单位向量,若向量
,则
与有序实数组
一一对应,称向量
的斜
坐标为
,记作
.
(1)若
,求
的斜
坐标;
(2)在平行六面体
中,
,建立“空间斜
坐标系”如下图所示.
①若
,求向量
的斜
坐标;
②若
,且
,求
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c4664eed9e1abab0ed6397c58d70e731.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d053b14c8588eee2acbbe44fc37a6886.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e81e59019989b7dc2fb59b037ef6e010.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/138c39673b579f1346c38398811105a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d1b8a88a16125366536cb4ad658e0cf1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cee4e3cf72016a2b908b9178b8317b84.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d1b8a88a16125366536cb4ad658e0cf1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cee4e3cf72016a2b908b9178b8317b84.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/971975007772deb92f837127a7936389.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d9fe31c74115f017c61dc7e6d78d5fac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d9cd8bbf47b69bbd7a6263b041290d11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
(2)在平行六面体
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a96b1713aa3c420848e9865afefa3fb5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/10/27/30f606bc-c728-4798-a6d6-a33bb22e85bf.png?resizew=181)
①若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/099edd3520292558184521a9af4e9064.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/253b99b8c8a45ace50b590cdd89b238a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
②若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bcc897340d513ba62e60b02e5ede30a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/59cbb23e8edee78010195fe66d3e55b8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5813dd9f2bd01a38d749247eccca5449.png)
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