a: Thay m=3 vào hệ phương trình, ta được:
\(\left\{{}\begin{matrix}\left(3-1\right)x+y=3\\x+\left(3-1\right)y=2\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}2x+y=3\\x+2y=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x+2y=6\\x+2y=2\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}4x+2y-x-2y=6-2\\x+2y=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}3x=4\\2y=2-x\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=\dfrac{4}{3}\\2y=2-\dfrac{4}{3}=\dfrac{2}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{4}{3}\\y=\dfrac{1}{3}\end{matrix}\right.\)