Hello,
[tex] \left \{ {{x-y=4} \atop {xy=2}} \right \\\\
\left \{ {{x=4+y} \atop {(4+y)y=2}} \right \\\\
\left \{ {{x=4+y} \atop {y^2+4y-2=0}} \right. \\\\
\Delta=4^2-4*1*(-2)=24=(2 \sqrt{6} )^2\\\\
y= \frac{-4+2 \sqrt{6} }{2}\ or\ y= \frac{-4-2 \sqrt{6} }{2}\\\\
y= -2+\sqrt{6} \ or\ y= -2- \sqrt{6}\\
\boxed{Sol=\{ (2+ \sqrt{6} ,-2+\sqrt{6} ),(2- \sqrt{6} ,-2-\sqrt{6} )\} }
[/tex]
