Which of the following is an integrating factor for the ODE y′+yx=x2y' + \frac{y}{x} = x^2y′+xy=x2?
μ(x)=x\mu(x) = xμ(x)=x
μ(x)=1x\mu(x) = \frac{1}{x}μ(x)=x1
μ(x)=x2\mu(x) = x^2μ(x)=x2
μ(x)=ex\mu(x) = e^xμ(x)=ex