a. \(\left\{{}\begin{matrix}3x+2y=8\\4x-3y=-12\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}-x+5y=20\\3x+2y=8\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=5y-20\\3.\left(5y-20\right)+2y=8\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=5y-20\\15y-60+2y=8\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=5.4-20\\y=4\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=0\\y=4\end{matrix}\right.\)
b. \(\left\{{}\begin{matrix}2x+5=-\left(x-y\right)\\6x+2y=-10\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}3x-y=-5\\6x+2y=-10\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}y=3x+5\\6x+2.\left(3x+5\right)=-10\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}y=3x+5\\6x+6x+10=-10\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}y=3.\left(-\frac{5}{3}\right)+5\\x=-\frac{5}{3}\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=-\frac{5}{3}\\y=0\end{matrix}\right.\)
