f(1-2x)=(1-x²)/x²
=1/x²-1
令z=1-2x
2x=1-z
x=(1-z)/2
f(z)=1/((1-z)/2)²-1
=4/(1-2z+z²)-1
=(4-(1-2z+z²))/(1-2z+z²)
=(3+2z-z²)/(1-2z+z²)
即:f(x)=(3+2x-x²)/(1-2x+x²)
f(1-2x)=(1-x²)/x²
=1/x²-1
令z=1-2x
2x=1-z
x=(1-z)/2
f(z)=1/((1-z)/2)²-1
=4/(1-2z+z²)-1
=(4-(1-2z+z²))/(1-2z+z²)
=(3+2z-z²)/(1-2z+z²)
即:f(x)=(3+2x-x²)/(1-2x+x²)