Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}m.cosx = m - 1 \Leftrightarrow co\,sx = \frac{{m - 1}}{m}\\ \Leftrightarrow - 1 \le \frac{{m - 1}}{m} \le 1\,\,\,\,\,\left( {m \ne 0} \right)\\ \Leftrightarrow \left\{ \begin{array}{l} - 1 \le \frac{{m - 1}}{m}\\\frac{{m - 1}}{m} \le 1\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}\frac{{m - 1}}{m} + 1 \ge 0\\1 - \frac{{m - 1}}{m} \ge 0\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}\frac{{2m - 1}}{m} \ge 0\\\frac{{ - 1}}{m} \ge 0\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}\left( {2m - 1} \right)m \ge 0\\m < 0\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}\left[ \begin{array}{l}m < 0\\m \ge \frac{1}{2}\end{array} \right.\\m < 0\end{array} \right. \Leftrightarrow m < 0\end{array}\)
