Đáp án:
b) m=-3
Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
x + my = 4\\
mx + 4y = 10 - m
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- mx - {m^2}y = - 4m\\
mx + 4y = 10 - m
\end{array} \right.\\
\to \left\{ \begin{array}{l}
\left( {4 - {m^2}} \right)y = 10 - 5m\\
x = 4 - my
\end{array} \right.\\
\to \left\{ \begin{array}{l}
\left( {2 - m} \right)\left( {2 + m} \right)y = 5\left( {2 - m} \right)\\
x = 4 - my
\end{array} \right.\\
a)DK:\left( {2 - m} \right)\left( {2 + m} \right) \ne 0 \to m \ne \pm 2\\
\to \left\{ \begin{array}{l}
y = \dfrac{5}{{m + 2}}\\
x = 4 - m.\dfrac{5}{{m + 2}} = \dfrac{{4m + 8 - 5m}}{{m + 2}}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
y = \dfrac{5}{{m + 2}}\\
x = \dfrac{{8 - m}}{{m + 2}}
\end{array} \right.\\
b)Do:y - 5x = - 4\\
\to \dfrac{5}{{m + 2}} - 5.\dfrac{{8 - m}}{{m + 2}} = - 4\\
\to 5 - 40 + 5m = - 4m - 8\\
\to 9m = - 27\\
\to m = - 3
\end{array}\)
