\left\{{{\frac{2x}{3}+\frac{4y}{5}=-2}\atop{\frac{x}{2}-\frac{y}{10}=2}}\right.
pierwsze równanie mnożymy przez 15, a drugie przez 10
\left\{{{5*2x+3*4y=-30}\atop{5x-y=20}}\right.
\left\{{{10x+12y=-30}\atop{5x-y=20}}\right.
\left\{{{10x+12y=-30}\atop{-y=20-5x}}\right.
\left\{{{10x+12y=-30}\atop{y=-20+5x}}\right.
\left\{{{10x+12y=-30}\atop{y=5x-20}}\right.
\left\{{{10x+12(5x-20)=-30}\atop{y=5x-20}}\right.
\left\{{{10x+60x-240)=-30}\atop{y=5x-20}}\right.
\left\{{{70x=-30+240}\atop{y=5x-20}}\right.
\left\{{{70x=210}\atop{y=5x-20}}\right.
\left\{{{x=3}\atop{y=5*3-20}}\right.
\left\{{{x=3}\atop{y=15-20}}\right.
\left\{{{x=3}\atop{y=-5}}\right.