P(X,Y)
PM/PN=√2
√[(x-1)^2+y^2]/ √[(x+1)^2+y^2]=√2
PM:y=kx+b,M(-1,0)
kx-y+K=0,N(1,0)
1=|K+K|/√(k^2+1)
|k|=1
x±y+1=0
x=-1,y=±2
PN:Y=X-1或y=-x+1
面积相等法比较简单