\(y'=\dfrac{m\left(m+1\right)-\left(4m+10\right)}{\left(x+m\right)^2}=\dfrac{m^2-3m-10}{\left(x+m\right)^2}\)
\(y'< 0;\forall x\in\left(-\infty;-2\right)\) khi và chỉ khi:
\(\left\{{}\begin{matrix}m^2-3m-10< 0\\-m\ge-2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}-2< m< 5\\m\le2\end{matrix}\right.\)
\(\Rightarrow-2< m\le2\)