$Ta$ $có$ $x(x-y)=\frac{3}{10}$ $(1)$
$y(x-y)=\frac{-3}{10}$ $(2)$
$Lấy$ $(1):(2)$ $ta$ $được$ $\frac{x}{y}$ $=-1$
$⇒x=-y$
$Ta$ $lại$ $có$ $x(x-y)=\frac{3}{10}$
$⇒$ $x(x+x)=\frac{3}{10}$
$⇒$ $2x^2=\frac{3}{10}$
$⇒$ $x^2=\frac{3}{20}$
$⇒$ $x=±\frac{√3}{√20}$
$⇒$ $y=±\frac{√3}{√20}$
$⇒$ \(\left[ \begin{array}{l}\left \{ {{x=\frac{√3}{√20}} \atop {y=-\frac{√3}{√20}}} \right.\\\left \{ {{x=-\frac{√3}{√20}} \atop {y=\frac{√3}{√20}}} \right.\end{array} \right.\)
