Từ pt dưới:
\(x^2+9y^2=6xy\Leftrightarrow x^2-6xy+9y^2=0\)
\(\Leftrightarrow\left(x-3y\right)^2=0\Leftrightarrow x-3y=0\Leftrightarrow x=3y\)
Thế lên pt trên: \(2.\left(3y\right)^2+y^2=19\)
\(\Leftrightarrow19y^2=19\Leftrightarrow y^2=1\Rightarrow\left[{}\begin{matrix}y=1\Rightarrow x=3\\y=-1\Rightarrow x=-3\end{matrix}\right.\)