\(x^2-xy+y+2=0\)
\(\Leftrightarrow\left(x-\dfrac{y}{2}\right)^2-\left(\dfrac{y}{2}-1\right)^2+3=0\)
\(\Leftrightarrow\left(x-\dfrac{y}{2}\right)^2-\left(\dfrac{y}{2}-1\right)^2=1-4\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-\dfrac{y}{2}\right)^2=1\\\left(\dfrac{y}{2}-1\right)^2=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}2x-y=2\\2x-y=-2\end{matrix}\right.\\\left[{}\begin{matrix}y=6\\y=-2\end{matrix}\right.\end{matrix}\right.\)
với y=6 \(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=2\end{matrix}\right.\)
với y=-2 \(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-2\end{matrix}\right.\)
vậy S=\(\left\{\left(4;6\right);\left(2;6\right);\left(0;-2\right);\left(-2;-2\right)\right\}\)
