Đáp án:
a. \(m \ne - 4\)
Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
mx + 2y = 4\\
2x - y = m
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = 2x - m\\
mx + 4x - 2m = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = 2x - m\\
\left( {m + 4} \right)x = 4 + 2m
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = \dfrac{{2m + 4}}{{m + 4}}\\
y = \dfrac{{4m + 8 - {m^2} - 4m}}{{m + 4}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = \dfrac{{2m + 4}}{{m + 4}}\\
y = \dfrac{{8 - {m^2}}}{{m + 4}}
\end{array} \right.\\
a.Ycbt \to m + 4 \ne 0\\
\to m \ne - 4\\
b.\left\{ \begin{array}{l}
x = \dfrac{{2m + 4}}{{m + 4}}\\
y = \dfrac{{8 - {m^2}}}{{m + 4}}
\end{array} \right.
\end{array}\)
