Đáp án:
$\begin{array}{l}
\left\{ \begin{array}{l}
4x - 4y = 2\\
- 2x + 2y = 2m
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
2x - 2y = 1\\
2x - 2y = - 2m
\end{array} \right.\\
\Rightarrow 1 = - 2m\\
\Rightarrow m = - \frac{1}{2}
\end{array}$
Vậy m=-1/2