\(xy+x+y+1=0\Leftrightarrow\left(x+1\right)\left(y+1\right)=0\Rightarrow\left[{}\begin{matrix}x=-1\\y=-1\end{matrix}\right.\)
- Với \(x=-1\Rightarrow y-y^2=-12\Leftrightarrow y^2-y-12=0\Rightarrow\left[{}\begin{matrix}y=-3\\y=4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}P=-28\\P=63\end{matrix}\right.\)
- Với \(y=-1\) tương tự