- Thay m = -1 vào hệ phương trình trên .
\(\left\{{}\begin{matrix}-x+2y=-1+1=0\\2x-y=-2-1=-3\end{matrix}\right.\) => \(\left\{{}\begin{matrix}x=2y\\2x-y=-3\end{matrix}\right.\) => \(\left\{{}\begin{matrix}x=2y\\4y-y=-3\end{matrix}\right.\)
=> \(\left\{{}\begin{matrix}x=2y\\3y=-3\end{matrix}\right.\)=> \(\left\{{}\begin{matrix}x=2y\\y=-1\end{matrix}\right.\) => \(\left\{{}\begin{matrix}x=2\left(-1\right)=-2\\y=-1\end{matrix}\right.\)