a: \(\Leftrightarrow\left\{{}\begin{matrix}3x=6\\x-y=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\)
b: \(\Leftrightarrow\left\{{}\begin{matrix}4x-6y=2\\4x+y=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-7y=-7\\2x-3y=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=1\\x=2\end{matrix}\right.\)
c: \(\Leftrightarrow\left\{{}\begin{matrix}3x+3+2x+4y=4\\4x+4-x-2y=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}5x+4y=1\\3x-2y=5\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}5x+4y=1\\6x-4y=10\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=-1\end{matrix}\right.\)
