Firstly, the focal coordinate formula of ellipse is used to calculate the focal coordinate of ellipse for F 1(- root number 2,0) and F2 (root number 2,0). Because ∠ PF 65438+F02 = 45 degrees, the triangle PF 65438+F02 is an isosceles triangle, and the point P is at the intersection of the Y axis and the ellipse, so that Y can be calculated with x=0.