\(\Leftrightarrow\left\{{}\begin{matrix}x^3-y^3=9\\3x^2+6y^2-3x+12y=0\end{matrix}\right.\)
\(\Rightarrow x^3-y^3-3x^2-6y^2+3x-12y=9\)
\(\Leftrightarrow x^3-3x^2+3x-1=y^3+6y^2+12y+8\)
\(\Leftrightarrow\left(x-1\right)^3=\left(y+2\right)^3\)
\(\Leftrightarrow x-1=y+2\)
\(\Leftrightarrow y=x-3\)
Thế xuống pt dưới ...