Đáp án:
$\begin{array}{l}
\tan \dfrac{{3x - \pi }}{5} = - 3\\
\Rightarrow \dfrac{{3x - \pi }}{5} = \arctan \left( { - 3} \right) + k\pi \\
\Rightarrow 3x - \pi = 5.\arctan \left( { - 3} \right) + 5k\pi \\
\Rightarrow x = \dfrac{\pi }{3} + \dfrac{5}{3}.\arctan \left( { - 3} \right) + \dfrac{{5k\pi }}{3}\\
Do:x \in \left( {\dfrac{{ - \pi }}{2};\dfrac{{7\pi }}{6}} \right)\\
\Rightarrow x = \dfrac{{\pi + 5\arctan \left( { - 3} \right)}}{3}
\end{array}$
