[tex]\it y=1-2x\ \ \ \ \ (*)\\ \\ 5x+2y=0\ \stackrel{(*)}{\Longrightarrow}5x+2(1-2x)=0 \Rightarrow 5x+2-4x=0\Rightarrow x+2=0 \Rightarrow x=-2\\ \\ \\ x=-2\ \stackrel{(*)}{\Longrightarrow} y=1-2\cdot(-2) \Rightarrow y=1+4 \Rightarrow y=5\\ \\ \\ S:\begin{cases}\ \it x=-2\\ \\ \it y=5\end{cases}[/tex]
