由y=(1-√x)/(1+√x)得y>-1,
y(1+√x)=1-√x,
(y+1)√x=1-y,
√x=(1-y)/(1+y),
x=[(1-y)/(1+y)]^2,
x,y互换就得所求的反函数为y=[(1-x)/(1+x)]^2(x>-1).