Giải các hệ phương trình sau1/  (left{ egin{array}{l}3x + y = 3\2x - y = 7end{array} ight.

* Hướng dẫn giải

1/ \(\left\{ \begin{array}{l}
3x + y = 3\\
2x - y = 7
\end{array} \right. <  =  > \left\{ \begin{array}{l}
5x = 10\\
3x + y = 3
\end{array} \right. <  =  > \left\{ \begin{array}{l}
x = 2\\
3.2 + y = 3
\end{array} \right. <  =  > \left\{ \begin{array}{l}
x = 2\\
y =  - 3
\end{array} \right.\)

2/ \(\left\{ \begin{array}{l}
x + 2y = 5\\
3x + 4y = 5
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
2x + 4y = 10\\
3x + 4y = 5
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x =  - 5\\
x + 2y = 5
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x =  - 5\\
y = 5
\end{array} \right.\)