Đáp án:
4>m>2
Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
x = 1 - y\\
2\left( {1 - y} \right) + my = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 1 - y\\
\left( {m - 2} \right)y = 2
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 1 - y\\
y = \dfrac{2}{{m - 2}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 1 - \dfrac{2}{{m - 2}}\\
y = \dfrac{2}{{m - 2}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = \dfrac{{m - 4}}{{m - 2}}\\
y = \dfrac{2}{{m - 2}}
\end{array} \right.\\
Do:x < 0;y > 0\\
\to \left\{ \begin{array}{l}
\dfrac{{m - 4}}{{m - 2}} < 0\\
\dfrac{2}{{m - 2}} > 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
m - 2 > 0\\
m - 4 < 0
\end{array} \right.\\
\to 4 > m > 2
\end{array}\)
