题目内容
若双曲线
的离心率等于
,直线
与双曲线
的右支交于
两点.
(1)求
的取值范围;
(2)若
,点
是双曲线
上一点,且
,求![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707836448.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707712997.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707727344.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707743514.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707743318.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707758423.png)
(1)求
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707774312.png)
(2)若
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707790634.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707805313.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707743318.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707836887.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707836448.png)
(1)
(2)
,![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707883512.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707852540.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707868574.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707883512.png)
试题分析:(1)由
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707899809.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707914701.png)
故双曲线
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707743318.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707946529.png)
设
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707961922.png)
由
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707961847.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707977924.png)
又直线与双曲线右支交于
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707758423.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240117080392241.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707852540.png)
(2)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708055419.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240117080861044.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240117081021424.png)
得
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708117805.png)
∴
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708133532.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708148526.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707852540.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707868574.png)
那么
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708195928.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708211961.png)
设
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708226679.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707836887.png)
∴
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240117082581395.png)
∴
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011708273749.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707883512.png)
故
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707868574.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824011707883512.png)
点评:直线与双曲线相交时常联立方程组,转化为关于x或y的二次方程,利用韦达定理设而不求的方法
再将所求问题用根与系数的关系的表示
![](http://thumb.zyjl.cn/images/loading.gif)
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