Tim m để hệ BPT sau có nghiệm a) 3x – 2 > -4x + 5 3x + m +2 < 0 b) x - 2 ≤ 0 m + x > 1 18/07/2021 Bởi Nevaeh Tim m để hệ BPT sau có nghiệm a) 3x – 2 > -4x + 5 3x + m +2 < 0 b) x - 2 ≤ 0 m + x > 1
Giải thích các bước giải: a, \(\begin{array}{l}\left\{ \begin{array}{l}3x – 2 > – 4x + 5\\3x + m + 2 < 0\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}7x > 7\\x < – \frac{{m + 2}}{3}\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}x > 1\\x < – \frac{{m + 2}}{3}\end{array} \right.\\ \Rightarrow – \frac{{m + 2}}{3} > 1\\ \Leftrightarrow \frac{{m + 2}}{3} > – 1\\ \Leftrightarrow m > – 5\\b,\\\left\{ \begin{array}{l}x – 2 \le 0\\m + x > 1\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}x \le 2\\x > 1 – m\end{array} \right.\\ \Rightarrow 1 – m \le 2\\ \Leftrightarrow m \ge – 1\end{array}\) Bình luận
Giải thích các bước giải:
a,
\(\begin{array}{l}
\left\{ \begin{array}{l}
3x – 2 > – 4x + 5\\
3x + m + 2 < 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
7x > 7\\
x < – \frac{{m + 2}}{3}
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x > 1\\
x < – \frac{{m + 2}}{3}
\end{array} \right.\\
\Rightarrow – \frac{{m + 2}}{3} > 1\\
\Leftrightarrow \frac{{m + 2}}{3} > – 1\\
\Leftrightarrow m > – 5\\
b,\\
\left\{ \begin{array}{l}
x – 2 \le 0\\
m + x > 1
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x \le 2\\
x > 1 – m
\end{array} \right.\\
\Rightarrow 1 – m \le 2\\
\Leftrightarrow m \ge – 1
\end{array}\)