名校
解题方法
1 . 为了求一个棱长为
的正四面体的体积,某同学设计如下解法.
解:构造一个棱长为1的正方体,如图1:则四面体
为棱长是
的正四面体,且有
.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/16/6db5d8bf-a942-4eb1-b74e-0d41be5b6734.png?resizew=583)
(1)类似此解法,如图2,一个相对棱长都相等的四面体,其三组棱长分别为
,
,
,求此四面体的体积;
(2)对棱分别相等的四面体
中,
,
,
.求证:这个四面体的四个面都是锐角三角形;
(3)有4条长为2的线段和2条长为
的线段,用这6条线段作为棱且长度为
的线段不相邻,构成一个三棱锥,问
为何值时,构成三棱锥体积最大,最大值为多少?
[参考公式:三元均值不等式
及变形
,当且仅当
时取得等号]
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf298f00799cbf34b4db26f5f63af92f.png)
解:构造一个棱长为1的正方体,如图1:则四面体
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68ac02c2f91cadb1e328bc6ab9b9c491.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf298f00799cbf34b4db26f5f63af92f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f6f878ffcff2ca25a434cbeea7d5c841.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/6/16/6db5d8bf-a942-4eb1-b74e-0d41be5b6734.png?resizew=583)
(1)类似此解法,如图2,一个相对棱长都相等的四面体,其三组棱长分别为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2967337e3fcb228dded64ab0c41a17e0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/50690dab38f4512eb72e18b7f86cf6f6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d4056761b8f826eeb6ad8c9a151d3c9c.png)
(2)对棱分别相等的四面体
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c220eadc312101e2fb89dfe920f7b30d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7de966c316db1013defc56372fcf814e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e8d2530e7023b2345c651e8f53629ff1.png)
(3)有4条长为2的线段和2条长为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
[参考公式:三元均值不等式
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1ffb6b373d2e672bb2afc8de547861a2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4849ff71159df2bb9099b26065d81e1f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/44acc0ee22dc4b7750e8be825e7c1355.png)
您最近一年使用:0次
2021-07-15更新
|
814次组卷
|
2卷引用:重庆市西南大学附属中学2020-2021学年高一下学期期末数学试题
2 . 我国古代数学著作《九章算术》中记载:斜解立方,得两堑堵.其意思是:一个长方体沿对角面一分为二,得到两个一模一样的堑堵.如图,在长方体
中,
,
,
,将长方体
沿平面
一分为二,得到堑堵
,下列结论正确的序号为______ .
①点C到平面
的距离等于
;
②
与平面
所成角的正弦值为
;
③堑堵
外接球的表面积为
;
④堑堵
没有内切球.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/efc6e4b936d7a800e839a30c3839574d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e65a3e478bb87d094e3a0af30dd10ae8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1f3e58edd1f900ca82bb2a3058293f52.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/679748eab882a6be0fefd2cc300349a4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2b5b14d74bdf9ed7c45b2e754b7ccc4f.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2024/4/2/203cf047-3c7e-43ff-9a8e-fb0157d5f7d4.png?resizew=233)
①点C到平面
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/679748eab882a6be0fefd2cc300349a4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81365a3726621b6557bd26f3a1a51cae.png)
②
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/588eb9393564a33552c4b2e8de837ca5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15a24acb11fac4bcf6a86e3e9223a48b.png)
③堑堵
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2b5b14d74bdf9ed7c45b2e754b7ccc4f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f08a01aed02ce1eaf1aaefaa0342b7ad.png)
④堑堵
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2b5b14d74bdf9ed7c45b2e754b7ccc4f.png)
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解题方法
3 . 《九章算术·商功》:“斜解立方,得两堑堵.斜解堑堵,其一为阳马,一为鳖臑.阳马居二,鳖臑居一,不易之率也.合两鳖臑三而一,验之以棊,其形露矣.”刘徽注:“此术臑者,背节也,或曰半阳马,其形有似鳖肘,故以名云.中破阳马,得两鳖臑,鳖臑之起数,数同而实据半,故云六而一即得.”
如图,在鳖臑ABCD中,侧棱AB⊥底面BCD;
(1)若
,
,
,试求异面直线AC与BD所成角的余弦值.
(2)若
,
,点P在棱AC上运动.试求
面积的最小值.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/7/22/84152742-e106-43ca-a408-c3b4449bce08.png?resizew=416)
如图,在鳖臑ABCD中,侧棱AB⊥底面BCD;
![](https://img.xkw.com/dksih/QBM/editorImg/2023/7/22/6476cb57-a508-4f63-868c-6a74790b42f7.png?resizew=301)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ced06b71073e1bb777f326f06016ce17.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef0402dd5ae3db10281f9f1e11738bcb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/037b342a682cbd4241855a243da3c016.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff9c7cbcc38b28d45c8539710e5b260a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a2e1ab67f8e48ad3340cf9d165cd75f0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acee03d4bb4667b6c345221b6c9b0fa4.png)
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名校
解题方法
4 . 设常数
.在棱长为1的正方体
中,点
满足
,点
分别为棱
上的动点(均不与顶点重合),且满足
,记
.以
为原点,分别以
的方向为
轴的正方向,建立如图空间直角坐标系
![](https://img.xkw.com/dksih/QBM/editorImg/2023/5/13/e06e4e4f-445b-442f-8e80-1e0f640affc9.png?resizew=217)
(1)用
和
表示点
的坐标;
(2)设
,若
,求常数
的值;
(3)记
到平面
的距离为
.求证:若关于
的方程
在
上恰有两个不同的解,则这两个解中至少有一个大于
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3eb6bf23a5a12e1ba5413594d7b1a57c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8a91c73ae980263c97742283b6b5852a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7789a500686c7a73770404ead6af0590.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cea77ba313fcc751481ac1ca214df3fc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/37e85b55b6ad43be1a03fc637e1d3429.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/651066b6919cab279373a8a1e1130839.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d68873c59a21b0cd408cdf2b47d51096.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1a14c388e1e2e5a2ff1ccf6caffbee0d.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/5/13/e06e4e4f-445b-442f-8e80-1e0f640affc9.png?resizew=217)
(1)用
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df64046e91b047037f19e4032e3b6de3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e15b268af571f9ecb37a864a08862814.png)
(2)设
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/200f24e682c93e02a87f3f9d57dc5d40.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d262b77e692c60e3c6b6afb610e8fe66.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df64046e91b047037f19e4032e3b6de3.png)
(3)记
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c28b88046022376b082b8a45c04577c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/77a90170d7ef5ff6d1d63517c166f7a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8a19e72906b84a1cb049167afdebdce0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7160d93f92089ef36f3dab809d3114b8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
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