x.y-2x+y+1=0
=>x.y-2x+y=-1
=>x.(y-2)+y=-1
=>x.(y-2)+y-2=(-1)-2
=>(y-2).(x+1)=-3
=>y-2;x+1 thuộc Ư(-3): {-1;1;-3;3}
ta có 4 trường hợp:
TH1: y-2 =1 ; x+1=-3
=> x=-4 ; y=3
TH2: y-2 =-1 ; x+1 =3
=> y=1 ; x=2
TH3: y-2 =3 ; x+1=-1
=> y=5 ; x=-2
TH4: y-2 =-3; x+1 = 1
=> y=-1 ; x=0