Vì x,y thuộc Z
(x+2y)( 2x-y)=7=1.7=7.1=(-1).(-7)=(-7).(-1)
$\left \{ {{x+2y=1} \atop {2x-y=7}} \right.$ <=>$\left \{ {{x=3} \atop {y=-1}} \right.$ ( thỏa)
$\left \{ {{x+2y=7} \atop {2x-y=1}} \right.$ <=>$\left \{ {{x=9/5} \atop {y=13/5}} \right.$ (loại)
$\left \{ {{x+2y=-1} \atop {2x-y=-7}} \right.$ <=>$\left \{ {{x=-3} \atop {y=1}} \right.$ ( thỏa)
$\left \{ {{x+2y=-7} \atop {2x-y=-1}} \right.$ <=>$\left \{ {{x=-9/5} \atop {y=-3/5}} \right.$ (loại)
Vậy (x;y)=(3;-1);(-3;1)
