Đáp án:
m=4
Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
x = y - 6\\
m\left( {y - 6} \right) + 2y = 18
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = y - 6\\
my - 6m + 2y = 18
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = y - 6\\
\left( {m + 2} \right)y = 18 + 6m
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = \dfrac{{18 + 6m}}{{m + 2}}\\
x = \dfrac{{18 + 6m - 6m - 12}}{{m + 2}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = \dfrac{{18 + 6m}}{{m + 2}}\\
x = \dfrac{6}{{m + 2}}
\end{array} \right.\\
DK:m \ne - 2\\
Có:2x + y = 9\\
\to \dfrac{{2.6}}{{m + 2}} + \dfrac{{18 + 6m}}{{m + 2}} = 9\\
\to 12 + 18 + 6m = 9m + 18\\
\to 3m = 12\\
\to m = 4\left( {TM} \right)
\end{array}\)
