\(a,\Leftrightarrow\Delta=16+4\left(m+4\right)\left(m-1\right)\ge0\\ \Leftrightarrow4m^2+12m\ge0\\ \Leftrightarrow4m\left(m+3\right)\ge0\Leftrightarrow\left[{}\begin{matrix}m\ge0\\m\le-3\end{matrix}\right.\\ b,\Leftrightarrow\Delta=\left(2m+1\right)^2-4\left(m^2+m-6\right)\ge0\\ \Leftrightarrow4m^2+4m+1-4m^2-4m+24\ge0\\ \Leftrightarrow25\ge0\)
Vậy PT luôn có nghiệm với mọi m
\(c,\Leftrightarrow\Delta=\left(m-1\right)^2+40\left(m-1\right)\ge0\\ \Leftrightarrow\left(m-1\right)\left(m+39\right)\ge0\\ \Leftrightarrow\left[{}\begin{matrix}m\ge1\\m\le-39\end{matrix}\right.\)
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