[tex]\it \begin{cases}\it 5x-y=7 \Rightarrow y=5x-7\ \ \ (*)\ (rela\c{\it t}ia\ de\ substitu\c{\it t}ie)\\ \\ \it x+2y=8 \stackrel{(*)}{\Longrightarrow}x+10x-14=8|_{+14}\Rightarrow 11x=22 \Rightarrow x=2\end{cases}\\ \\ \\ x=2\ \stackrel{(*)}{\Longrightarrow}\ y=10-7 \Rightarrow y=3\\ \\ S=\{(2,\ 3)\}[/tex]
