\(\Leftrightarrow\left\{{}\begin{matrix}2\left(x+y\right)+6xy=2+8\sqrt{2}\\3x^2+3y^2=9\end{matrix}\right.\)
\(\Rightarrow3\left(x+y\right)^2+2\left(x+y\right)=11+8\sqrt{2}\)
\(\Leftrightarrow3\left(x+y\right)^2+2\left(x+y\right)-11-8\sqrt{2}=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+y=1+\sqrt{2}\\x+y=\frac{-3-5\sqrt{2}}{3}\end{matrix}\right.\)
Thế vào pt đầu...