dat $\sqrt{x-y}=a\geq 0;\left| {x-2y} \right|=b\geq0=>$pt$\Leftrightarrow \begin{cases}a=9-b \\ b^2-2a^2=41 \end{cases}$tu pt tren the xuong ta co $b^2-2(9-b)^2=41=>b=7=>a=2;b=29=>a=-20(l)$
$a=2=>x=y+4$ thay vao b ta co $\left| {4-y} \right|=7=>y=-3=>x=1$
hoac $y=11=>x=15$
kl.........