Giải thích các bước giải:
\(\begin{array}{l}
DK:\left( {m + 4} \right){x^2} - \left( {m - 4} \right)x - 2m + 1 \ge 0\\
\Leftrightarrow \left\{ \begin{array}{l}
m \ge - 4\\
{m^2} - 8m + 16 - 4\left( {m + 4} \right)\left( {1 - 2m} \right) \le 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m \ge - 4\\
{m^2} - 8m + 16 - 4\left( { - 2{m^2} - 7m + 4} \right) \le 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m \ge - 4\\
{m^2} - 8m + 16 + 8{m^2} + 28m - 16 \le 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m \ge - 4\\
m \in \left[ { - \frac{{20}}{9};0} \right]
\end{array} \right.\\
\to m \in \left[ { - \frac{{20}}{9};0} \right]
\end{array}\)