[tex]\it \begin{cases}\it x-\sqrt2y=3 \Rightarrow x-3=\sqrt2y \Rightarrow \sqrt2y=x-3\ \ \ \ \ (*)\\ \\ \it -3x+2\sqrt2y=-7\end{cases}\\ \\ \\ \it -3x+2\sqrt2y=-7\ \stackrel{(*)}{\Longrightarrow}\ -3x+2(x-3)=-7 \Rightarrow -3x+2x-6=-7\Rightarrow\\ \\ \Rightarrow -6+7=3x-2x\Rightarrow 1=x\Rightarrow x=1[/tex]
[tex]\it x=1\ \stackrel{(*)}{\Longrightarrow}\ \sqrt2y=1-3 \Rightarrow \sqrt2y=-2 \Rightarrow \sqrt2y=-\sqrt2\cdot\sqrt2|_{:\sqrt2} \Rightarrow \\ \\ \Rightarrow y=-\sqrt2\\ \\ \\ S=\{(1,\ \ -\sqrt2)\}[/tex]
