Consider a linear ordinary differential equation: $\frac{dy}{dx}+p\left ( x \right )y=r\left ( x \right )$.  Functions $p\left ( x \right )$ and $r\left ( x \right )$ are defined and have a continuous first derivative. The integrating factor of this equation is non-zero. Multiplying this equation by its integrating factor converts this into a:

1. Homogeneous differential equation
2. Non-linear differential equation
3. Second order differential equation
4. Exact differential equation