向量PF1*向量PF2 的最大值在P在椭圆左右顶点时取得:
(a-c)*(a+c)=4/3
=> a^2-c^2 = 4/3
向量PF1*向量PF2 的最小值在P在椭圆上下顶点时取得:
(-c,-b)*(c,-b)=-4/3
=> b^2-c^2 = -4/3
又:c^2=a^2-b^2
=> a^2=4 b^2=4/3
=> x^2/4 + y^2/(4/3) = 1
向量PF1*向量PF2 的最大值在P在椭圆左右顶点时取得:
(a-c)*(a+c)=4/3
=> a^2-c^2 = 4/3
向量PF1*向量PF2 的最小值在P在椭圆上下顶点时取得:
(-c,-b)*(c,-b)=-4/3
=> b^2-c^2 = -4/3
又:c^2=a^2-b^2
=> a^2=4 b^2=4/3
=> x^2/4 + y^2/(4/3) = 1