Question

\(\left\{{}\begin{matrix}3x+y=3\\2x-y=7\end{matrix}\right.\)

\(\left\{{}\begin{matrix}-3x-y=-8\\7x-2y=23\end{matrix}\right.\)

Answer 1

\(\left\{{}\begin{matrix}3x+y=3\\2x-y=7\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}3x+y+2x-y=3+7\\2x-y=7\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}5x=10\\y=2x-7\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=2\\y=2\cdot2-7=-3\end{matrix}\right.\)

\(\left\{{}\begin{matrix}-3x-y=-8\\7x-2y=23\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}3x+y=8\\7x-2y=23\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}6x+2y=16\\7x-2y=23\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}13x=39\\3x+y=8\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=3\\y=8-3x=8-3\cdot3=-1\end{matrix}\right.\)