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[几何] 椭圆离心率，双球

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guanmo1 Posted 2016-12-12 16:20 |Read mode

QQ截图20161212165008.jpg

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kuing Posted 2016-12-12 17:01

时间关系就懒得画图了，网上随便搜了一个图：

QQ截图20161212165712.jpg

QQ截图20161212165712.jpg

$PF_1+PF_2=K_1K_2$，对于本题易知 $K_1K_2=16$，所以 $a=8$，又显然 $b=2$，从而 $e=\sqrt{15}/4$。

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敬畏数学 Posted 2016-12-12 17:43

Dandelin双球画得很漂亮啊！

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