Để BPT nghiệm đúng với mọi x thì:
a/ \(\left\{{}\begin{matrix}2m^2-3m-2< 0\\\Delta'=\left(m-2\right)^2+2m^2-3m-2\le0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2m^2-3m-2< 0\\3m^2-7m+2\le0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}-\frac{1}{2}< m< 2\\\frac{1}{3}\le m\le2\end{matrix}\right.\)
\(\Rightarrow\frac{1}{3}\le m< 2\)
b/ \(\left(m+4\right)x^2-2mx+2m-6< 0\)
\(\left\{{}\begin{matrix}m+4< 0\\\Delta'=m^2-\left(m+4\right)\left(2m-6\right)< 0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}m< -4\\-m^2-2m+24< 0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}m< -4\\\left[{}\begin{matrix}m< -6\\m>4\end{matrix}\right.\end{matrix}\right.\) \(\Rightarrow m< -6\)
