题目内容
设F1,F2是双曲线C,
-
=1(a>0,b>0)的两个焦点.若在C上存在一点P,使PF1⊥PF2,且∠PF1F2=30°,则C的离心率为 .
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324078445.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324093476.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324093344.png)
设点P在双曲线右支上,
由题意,在Rt△F1PF2中,
|F1F2|=2c,∠PF1F2=30°,
得|PF2|=c,|PF1|=
c,
根据双曲线的定义:|PF1|-|PF2|="2a,("
-1)c=2a,
e=
=
=
+1.
由题意,在Rt△F1PF2中,
|F1F2|=2c,∠PF1F2=30°,
得|PF2|=c,|PF1|=
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324093344.png)
根据双曲线的定义:|PF1|-|PF2|="2a,("
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324093344.png)
e=
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324140354.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324156510.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824041324093344.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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