\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=-3\\2x+6y=8\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-7y=-11\\2x-y=-3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{11}{7}\\2x=-3+y=\dfrac{11}{7}-3=-\dfrac{10}{7}\end{matrix}\right.\)
hay (x,y)=(-5/7;11/7)
\(\left\{{}\begin{matrix}2x-y=-3\\x+3y=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=2x+3\\x+6x+9=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=2x+3\\7x=4-9=-5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=2.\left(-\dfrac{5}{7}\right)+3\\x=-\dfrac{5}{7}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{11}{7}\\x=-\dfrac{5}{7}\end{matrix}\right.\)
`{(2x-y=-3),(x+3y=4):}`
`<=>{(6x-3y=-9),(x+3y=4):}`
`<=>{(7x=-5),(x+3y=4):}`
`<=>{(x=-5/7),(-5/7+3y=4):}`
`<=>{(x=-5/7),(y=11/7):}`
6x - 3y = 9
x + 3y = 4
7x = 13
x + 3y = 4
x = 13/7
y = 5/7
