Ta có: $x-y=2\left( x+y \right)\Rightarrow x-y=2x+2y\Rightarrow x-2x=2y+y\Rightarrow -x=3y\Rightarrow x=-3y$
Thay $x=-3y$ vào $x-2y=\frac{3x}{y}$ ta được $-3y-2y=\frac{3\left( -3y \right)}{y}\Rightarrow -5y=\frac{-9y}{y}\Rightarrow -5y=-9\Rightarrow y=\frac{9}{5}$
$\Rightarrow x=-3.\frac{9}{5}=\frac{-27}{5}$
Vậy $\left( x;y \right)=\left( \frac{-27}{5};\frac{9}{5} \right)$