（x^2-4x+1)/(x^2-1)=2x/(x+1)
x^2-4x+1=2x(x-1)
x^2-4x+1=2x^2-2x
-x^2-2x+1=0
x^2+2x-1=0
x^2+2x+1=2
(x+1)^2=2
x+1=±√2
x=-1±√2.