The integrating factor f(x), to solve ODE (x-1)y^(')-(x²-1)y=x-1, is ________.
1) f(x)=e^((x³)/(3)-x)
2) f(x)=e^((-x³)/(3)-x)
3) f(x)=e^((x²)/(2)-x)
4) f(x)=e^((-x²)/(2))