Solution (source code)

= Solution

Rewrite the <linear ordinary differential equation> as $y'+y=e^{3x}$. Multiplication by its <integrating factor> $e^x$ gives $(e^xy)'=e^{4x}$. Integrating yields
$$
\boxed{y(x)=\frac14e^{3x}+Ce^{-x}.}
$$
The <general solution> consists of this <particular solution> and the <homogeneous solution> $Ce^{-x}$.