\(\left\{{}\begin{matrix}2x-y=-3\\x+3y=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=-3\\2x+6y=8\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=-3\\\left(2x-2x\right)+\left(-y-6y\right)=-3-8\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=-3\\-7y=-11\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=-3\\y=\dfrac{11}{7}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x-\dfrac{11}{7}=-3\\y=\dfrac{11}{7}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x=-\dfrac{10}{7}\\y=\dfrac{11}{7}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{5}{7}\\y=\dfrac{11}{7}\end{matrix}\right.\)
Vậy hệ pt có nghiệm duy nhất \(\left(x;y\right)=\left(-\dfrac{5}{7};\dfrac{11}{7}\right)\)
