The integrating factor of the linear differentia; equation $\frac{dy}{dx}+P(x)y=Q(x)$ is :

$\int\limits^{}_{e}Q(x)dx$ $\int\limits^{}_{e}P(x).Q(x)dx$ $∫P(x)dx$ $\int\limits^{}_{e}P(x)dx$

$\int\limits^{}_{e}P(x)dx$

Linear integrating factor is $\int\limits^{}_{e}P(x)dx$