Question

椭圆的左右焦点分别为F1,F2,P为椭圆上一点 ,c^2<|PF1||PF2|cos∠F1PF2<3c^2,求离心率的取值范围

卧式椭圆

Answer 1

取值范围是[√2/2 ，1]

Answer 2

Clue: Since point P is randomly designated. Think extreme situations, when P is separately at the X axis and Y axis.

Answer 3

离心率范围：√3-1<e<1，不知是否正确？