4X2+9Y2=36 a^2=9 b^2=4a=3 b=2b^2=a^2-c^2 c=根号5f1=(-√5,0)f2=(√5,0)p(x,y)kpf1*kpf2=-1y^2/(x^2-5)=-1,4X2+9Y2=36x=+/3/√5  y=+/-4/√5p(3/√5,4/√5)(3/√5,-4/√5)(-3/√5,4/√5)(-3/√5,-4/√5)

是∠F1PF2=90°则PF1^2+PF2^2=F1F2^2(x-√5)^2+y^2+(x+√5)^2+y^2=(2√5)^2则x^2+y^2=5,x^2/9+y^2/4=1联立，解得P的四个坐标(3√5/5,4√5/5),(3√5/5,-4√5/5),(-3√5/5,4√5/5),(-3√5/5,-4√5/5).

以f1 f2为端点做圆求他与椭圆交点。4个