\(\left\{{}\begin{matrix}x+3y=-2\\5x-4y=11\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}5x+15y=-10\\5x-4y=11\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}19y=-21\\x+3y=-2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{21}{19}\\x+3\cdot\dfrac{-21}{19}=-2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{21}{19}\\x=\dfrac{25}{19}\end{matrix}\right.\)
Vậy HPT có nghiệm duy nhất (x;y) = \(\left(\dfrac{25}{19};-\dfrac{21}{19}\right)\)
`{(x+3y=-2), (5x - 4y =11):}`
`<=> {(5x + 15y =-10), (5x - 4y = 11):}`
`<=> {(5x + 15y - 5x + 4y = -21), (x + 3y = -2):}`
`<=> {(19y = -21), (x + 3y = -2):}`
`<=> {(y = -21/19), (x= 25/19):}`
