\(\left\{{}\begin{matrix}4x+7y=16\\4x-3y=-24\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}10y=40\\4x-3y=-24\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}y=4\\4x-3.4=-24\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}y=4\\4x-12=-24\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}y=4\\4x=-12\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}y=4\\x=-3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}10y=40\\4x+7y=16\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=4\\4x=16-7y=16-7\cdot4=-12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-3\\y=4\end{matrix}\right.\)
