\(\left\{{}\begin{matrix}2x+y=5\\4x-y=7\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}4x+2y=10\\4x-y=7\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x+y=5\\\left(4x-4x\right)+\left(2y+y\right)=10-7\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x+y=5\\3y=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x+y=5\\y=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x+1=5\\y=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x=4\\y=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\)
Vậy hệ pt có nghiệm duy nhất \(\left(x;y\right)=\left(2;1\right)\)
