如图1,用一个平面去截圆锥,得到的截口曲线是椭圆.许多人从纯几何的角度对这个问题进行研究,其中比利时数学家Germinal dandelion(1794-1847)的方法非常巧妙,极具创造性.在圆锥内放两个大小不同的球,使得它们分别与圆锥的侧面、截面相切,两个球分别与截面切于
、
,在截口曲线上任取一点
,过
作圆锥的母线,分别与两个球切于
、
,由球和圆的几何性质,可以知道,
,
,于是
,由
、
的产生方法可知,它们之间的距离
是定值,由椭圆定义可知,截口曲线是以
、
为焦点的椭圆.如图2,一个半径为1的球放在桌面上,桌面上方有一点光源
,则球在桌面上的投影是椭圆,已知
是椭圆的长轴,
垂直于桌面且与球相切,
,则椭圆的离心率为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
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![](https://img.xkw.com/dksih/QBM/editorImg/2023/11/10/4af1926f-8781-4cde-a7f0-f7bb9966926d.png?resizew=365)
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更新时间:2023-11-10 20:52:05
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【推荐1】表面积为
的球面上有三点A、B、C,∠ACB=60°,AB=
,则球心到截面ABC的距离及B、C两点间球面距离最大值分别为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6faf2435da64db21c00fbe489c8f943f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a7ffe8515ff6183c1c7775dc6f94bdb8.png)
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解题方法
【推荐2】在三棱锥
中,
两两垂直,且
,半径为1的球
在该三棱锥内部且与面
、面
、面
均相切.若平面
与球
相切,则三棱锥
的外接球被平面
所截得的截面面积的最小值为( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/891579e7c231584a8e16b8eeff79888e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/479cb5a34cc5f7bf4c4fb3d1c2b52212.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/831d40ae84e37a5939ccd15187d5e2a2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7abd284f76d9f5769bc189508ce2572b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ca67a5b8f69507c8b80379e86f90a8ce.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/891579e7c231584a8e16b8eeff79888e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
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【推荐1】已知点
、
分别是椭圆
的左、右焦点,过
的直线交椭圆于A、B两点,O为坐标原点,且满足
,
,则该椭圆的离心率是( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f5076289823db419f94e9c0c8f4aafd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a3fb78c5f885034612c0e030b920143d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/48da128547c4cf9745e8e4b99988a3db.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a3fb78c5f885034612c0e030b920143d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c1cbbd084e29b7c2a851e06b47ed74c0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/28cfa69d3c33441e62a0b5cecfa4e905.png)
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名校
【推荐2】设椭圆
的两个焦点是
,
,过点
的直线与椭圆
交于点
,
,若
,且
,则椭圆
的离心率等于( )
![](https://img.xkw.com/dksih/QBM/editorImg/2022/12/2/e31e0e32-a10e-43d7-aaa5-85b4cd24f1dc.png?resizew=172)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f5076289823db419f94e9c0c8f4aafd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a3fb78c5f885034612c0e030b920143d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f5076289823db419f94e9c0c8f4aafd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/093bec291d374725e9e4810847568a72.png)
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