[tex]x(x+y+z)=6\\
y(x+y+z)=12\\
z(x+y+z)=18\\
\\+ \\
(x+y+z)(x+y+z)=36 \\ (x+y+z)^{2} = 36\\(x+y+z)= \sqrt{36} \\ (x+y+z)=6 \\sau\\(x+y+z)=-6\\
1. (x+y+z)=6\\
x(x+y+z)=6=\ \textgreater \ x=1\\
y(x+y+z)=12=\ \textgreater \ y=2 \\
z(x+y+z)=18=\ \textgreater \ z=3\\ \\
2. (x+y+z)=-6\\
x(x+y+z)=6=\ \textgreater \ x=-1\\
y(x+y+z)=12=\ \textgreater \ y=-2\\
z(x+y+z)=18=\ \textgreater \ z=-3\\
S= {(1; 2; 3); (-1; -2; -3)}
[/tex]
