Đáp án:
d) \(\left\{ \begin{array}{l}
x = 3\\
y = - 2
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
B1:\\
a)\left\{ \begin{array}{l}
2x - y = 3\\
x + 2y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
4x - 2y = 6\\
x + 2y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
5x = 10\\
y = 2x - 3
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 2\\
y = 1
\end{array} \right.\\
b)\left\{ \begin{array}{l}
4x - 5y = 3\\
3x - y = 6
\end{array} \right.\\
\to \left\{ \begin{array}{l}
4x - 5y = 3\\
- 15x + 5y = - 30
\end{array} \right.\\
\to \left\{ \begin{array}{l}
- 11x = - 27\\
y = 3x - 6
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = \dfrac{{27}}{{11}}\\
y = \dfrac{{15}}{{11}}
\end{array} \right.\\
c)\left\{ \begin{array}{l}
4x - 2y = - 6\\
- 4x + 2y = 6
\end{array} \right.\\
\to \left\{ \begin{array}{l}
0x = 0\left( {ld} \right)\\
4x - 2y = - 6
\end{array} \right.
\end{array}\)
⇒ Phương trình vô số nghiệm
\(\begin{array}{l}
d)\left\{ \begin{array}{l}
4x + 3y = 6\\
6x + 3y = 12
\end{array} \right.\\
\to \left\{ \begin{array}{l}
2x = 6\\
y = 4 - 2x
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 3\\
y = - 2
\end{array} \right.
\end{array}\)
