Solution (source code)

= Solution

Use the <method of undetermined coefficients> with a <particular solution> $Ke^{-\sqrt3x}$. The differential operator multiplies this <exponential function> by $3-3+3=3$. Matching the forcing coefficient gives $3K=1$, hence
$$
\boxed{y_{p,1}(x)=\frac13e^{-\sqrt3x}.}
$$