f'(x) = (2x-4)/(x-1) - (x^2-4x+7)/(x-1)(x-1) = [(2x-4)(x-1)-(x^2-4x+7)]/(x-1)^2
= (2x^2-6x+4-x^2+4x-7)/(x-1)^2 = (x^2-2x-3)/(x-1)^2
x>3 或者x