x平方-2x/x平方-1除以[(x-1)-(2x-1/x+1)]
=[x(x-2)/(x+1)(x-1)]/[(x^2-1-2x+1)/(x+1)]
=x(x-2)/(x+1)(x-1)×(x+1)/x(x-2)
=1/(x-1)
=1/(2+根号2-1）
=1/(根号2+1）
=根号2-1