Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}
a.m = 2\\
Hpt \to \left\{ \begin{array}{l}
x - 2y = 5\\
2x - y = 4
\end{array} \right. \to \left\{ \begin{array}{l}
x = 1\\
y = - 2
\end{array} \right.\\
m = 3\\
Hpt \to \left\{ \begin{array}{l}
x - 2y = 5\\
3x - y = 4
\end{array} \right. \to \left\{ \begin{array}{l}
x = \frac{3}{5}\\
y = \frac{{ - 11}}{5}
\end{array} \right.
\end{array}\)
b. Để hpt có nghiệm
\( \Leftrightarrow \frac{1}{m} \ne 2 \to m \ne \frac{1}{2}\)
c. TH1:x=y
\(Hpt \to \left\{ \begin{array}{l}
x - 2x = 5\\
mx - x = 4
\end{array} \right. \to \left\{ \begin{array}{l}
x = - 2\\
m = - 1
\end{array} \right.\)
TH2: -x=y
\(Hpt \to \left\{ \begin{array}{l}
x + 2x = 5\\
mx + x = 4
\end{array} \right. \to \left\{ \begin{array}{l}
x = \frac{5}{3}\\
m = \frac{7}{5}
\end{array} \right.\)
