.设F1、F2为椭圆=1(a>b>0)的左右焦点,过F2作椭圆长轴的垂线交

.设F1、F2为椭圆=1(a>b>0)的左右焦点,过F2作椭圆长轴的垂线交椭圆于点P,若∠PF1F2=60°,则椭圆的离心率是      

答案

 2﹣ 

【考点】椭圆的简单性质.

【专题】数形结合;方程思想;数学模型法;圆锥曲线的定义、性质与方程.

【分析】把x=c代入可得,解得y,利用∠PF1F2=60°,即可得出.

【解答】解:把x=c代入可得,解得y=±

∵∠PF1F2=60°,

=

化为e2+2e﹣1=0,又0<e<1,

解得e=2﹣

故答案为:2﹣

【点评】本题了考查了椭圆的标准方程及其性质、直角三角形的边角关系,考查了推理能力与计算能力,属于中档题.

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