\(\begin{array}{l}
b)\,DK:\,\left\{ \begin{array}{l}
x \ge - m\\
x \ge \dfrac{{m - 1}}{2}
\end{array} \right.\\
TH1:\,\, - m \ge \dfrac{{m - 1}}{2} \Leftrightarrow - 2m \ge m - 1 \Leftrightarrow m \le \dfrac{1}{3}\\
\Rightarrow D = \left[ { - m; + \infty } \right)\\
ycbt \Rightarrow - m \le 0 \Rightarrow m \ge 0 \Rightarrow 0 \le m \le \dfrac{1}{3}\\
TH2:\,\dfrac{{m - 1}}{2} > - m \Leftrightarrow m - 1 > - 2m \Leftrightarrow 3m > 1 \Leftrightarrow m > \dfrac{1}{3}\\
\Rightarrow D = \left[ {\dfrac{{m - 1}}{2}; + \infty } \right)\\
ycbt \Rightarrow \dfrac{{m - 1}}{2} \le 0 \Leftrightarrow m \le 1 \Rightarrow \dfrac{1}{3} < m \le 1\\
Vậy\,\,0 \le m \le 1
\end{array}\)
