Đáp án:
$\begin{array}{l}
\left\{ \begin{array}{l}
2x + 3y = m\\
25x - 3y = 3
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
27x = m + 3\\
2x + 3y = m
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
x = \frac{{m + 3}}{{27}}\\
y = \frac{{m - 2x}}{3} = \frac{{m - \frac{{2m + 6}}{{27}}}}{3} = \frac{{25m - 6}}{{81}}
\end{array} \right.\\
Do:\left\{ \begin{array}{l}
x > 0\\
y < 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
\frac{{m + 3}}{{27}} > 0\\
\frac{{25m - 6}}{{81}} < 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
m > - 3\\
m < \frac{6}{{25}}
\end{array} \right.\\
Vậy\, - 3 < m < \frac{6}{{25}}
\end{array}$
