\(x^2=2y^2\Leftrightarrow x^2-2y^2=0\\ \Leftrightarrow\left(x-y\right)\left(x+y\right)-y^2=0\)
\(\Rightarrow\left[{}\begin{matrix}\left(x-y\right)\left(x+y\right)=0\\y^2=0\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=0\\y=0\end{matrix}\right.\)
vậy x=0; y=0