[tex]\bf 3tan(2x)=-3\implies tan(2x)=\cfrac{-3}{3}\implies tan(2x)=-1
\\\\\\
tan^{-1}[tan(2x)]=tan^{-1}(-1)\implies 2x=tan^{-1}(-1)
\\\\\\
2x=
\begin{cases}
\frac{3\pi }{4}\\\\
\frac{7\pi }{4}
\end{cases}\implies
\begin{cases}
2x=\cfrac{3\pi }{4}\implies \measuredangle x=\cfrac{3\pi }{8}\\\\
2x=\cfrac{7\pi }{4}\implies \measuredangle x=\cfrac{7\pi }{8}
\end{cases}[/tex]
