Ok so heres the question, il put it into a picture to help better
$\displaystyle \begin{array}{lrcl}
{} & 3\tan^3{x}-\tan{x} &=& 0\\\\
\Rightarrow & (3\tan^2{x}-1)\tan{x} &=& 0\\\\
\end{array}$
$\displaystyle \Rightarrow\ 3\tan^2{x}-1=0\ \mbox{ or }\tan{x}=0$
$\displaystyle \Rightarrow\ \tan{x}=\pm\frac{1}{\sqrt{3}}\ \mbox{ or }\tan{x}=0$
Now you carry on from there.