Question

Answer 1

Thay x = 3 ; y = -1 vào ta được 

\(\left\{{}\begin{matrix}3a-b=3\\3b+a=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}9a-3b=9\\a+3b=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}10a=20\\b=3a-3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=2\\b=3\end{matrix}\right.\)