Solution (source code)

= Solution

A linear <polynomial> trial $y=ux+v$ has $y'=u$ and $y''=0$. Substituting gives $3ux+(\sqrt3u+3v)=x$, so $u=1/3$ and $v=-\sqrt3/9=-1/(3\sqrt3)$. Thus a <particular solution> is
$$
\boxed{y_{p,2}(x)=\frac x3-\frac1{3\sqrt3}.}
$$