b, 3x+4y-xy=16
3x-xy+4y-12=16-12
x(3-y)+4(y-3)=16-12
x(3-y)-4(3-y)=16-12
(x-4)(3-y)=4
TH1: $\left \{ {{x-4=1} \atop {3-y=4}} \right.$ ⇒$\left \{ {{x=5} \atop {y=-1}} \right.$
TH2: $\left \{ {{x-4=-1} \atop {3-y=-4}} \right.$ ⇒$\left \{ {{x=3} \atop {y=7}} \right.$
Th3: $\left \{ {{x-4=2} \atop {3-y=2}} \right.$ ⇒$\left \{ {{x=6} \atop {y=1}} \right.$
TH4: $\left \{ {{x-4=-2} \atop {3-y=-2}} \right.$ ⇒$\left \{ {{x=2} \atop {y=5}} \right.$
TH5: $\left \{ {{x-4=4} \atop {3-y=1}} \right.$ ⇒$\left \{ {{x=8} \atop {y=2}} \right.$
TH6: $\left \{ {{x-4=-4} \atop {3-y=-1}} \right.$ ⇒$\left \{ {{x=0} \atop {y=4}} \right.$
Vì x∈Z
Vậy x∈{5;3;6;2;8;0}
