\(\dfrac{-2\left(m+4\right)}{m+1}< 0\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}-2\left(m+4\right)< 0\\m+1>0\end{matrix}\right.\\\left\{{}\begin{matrix}-2\left(m+4\right)>0\\m+1< 0\end{matrix}\right.\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}m+4>0\\m+1>0\end{matrix}\right.\\\left\{{}\begin{matrix}m+4< 0\\m+1< 0\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}m>-4\\m>-1\end{matrix}\right.\\\left\{{}\begin{matrix}m< -4\\m< -1\end{matrix}\right.\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}m>-1\\hoặc\\m< -4\end{matrix}\right.\) vậy \(m>-1\) hoặc \(m< -4\)
