设P(x,y) F1(-√2,0) F2(√2,0)
kPF1=y/(x-√2)
kPF2=y/(x+√2)
kPF1*kPF2=y^2/(x^2-2)=-1
y^2+x^2=2
x^2-y^2=1
2x^2=3
x1=-√6/2 y=√2/2或y=-√2/2
x2=√6/2 y=√2/2或y=-√2/2
所以P点有四个,坐标为(±√6/2,±√2/2)