[tex]\begin{cases}xy+x^2=0\\ y^2+2xy+x^2=0\end{cases}\Leftrightarrow \begin{cases}xy+x^2=0\\ (y+x)^2=0\end{cases}\Leftrightarrow \begin{cases}x(y+x)=0\\ y+x=0\end{cases}\Rightarrow y=-x[/tex]