[tex]a) \ \left \{ {{\ 2x \ + \ y \ = \ 0} \atop {\ x \ - \ y \ = \ -6}} \right.[/tex]
[tex]+ \left \{ {{ \ 2x \ + \ y \ = \ 0} \atop { \ x \ - \ y \ = \ -6}} \right.[/tex]
[tex]3x=-6 \ \ \ \ \ \ \ \ /:3[/tex]
[tex]x=-2[/tex]
[tex]2x+y=0[/tex]
[tex]2*(-2)+y=0[/tex]
[tex]y = 4[/tex]
[tex]\left \{ {{ \ x \ = \ -2} \atop { \ y \ = \ 4}} \right.[/tex]
[tex]b) \ \left \{ {{ \ 4x \ + \ y \ = \ 13 \ \ \ / \ * \ (-3)} \atop {x \ + \ 3y \ = \ 6}} \right.[/tex]
[tex]+\left \{ {{ \ -12x \ - \ 3y \ = \ -39} \atop {x \ + \ 3y \ = \ 6}} \right.[/tex]
[tex]-11x=-33 \ \ \ \ \ \ \ \ /:(-11)[/tex]
[tex]x=3[/tex]
[tex]x+3y=6[/tex]
[tex]3 + 3y=6[/tex]
[tex]3y = 3 \ \ \ \ \ \ \ /:3[/tex]
[tex]y=1[/tex]
[tex]\left \{ {{ \ x \ = \ 3} \atop { \ y \ = \ 1}} \right.[/tex]
