wszystko zależy od tego jak odczytać drugie równanie…
\left \{ {{-x+2y=7} \atop {x-\frac{1}{3}y=-2}} \right.
\left \{ {{-x=7-2y} \atop {x-\frac{1}{3}y=-2}} \right.
\left \{ {{x=-7+2y} \atop {-7+2y-\frac{1}{3}y=-2}} \right.
\left \{ {{x=-7+2y} \atop {1\frac{2}{3}y=-2+7}} \right.
\left \{ {{x=-7+2y} \atop {1\frac{2}{3}y=5}} \right.
\left \{ {{x=-7+2y} \atop {5y=15}} \right.
\left \{ {{x=-7+2y} \atop {y=3}} \right.
\left \{ {{x=-7+2*3} \atop {y=3}} \right.
\left \{ {{x=-7+6} \atop {y=3}} \right.
\left \{ {{x=-1} \atop {y=3}} \right.