a) xy -2x-y = -2
xy -2x -y +2 = 0
x(y-2) - (y-2)=0
(y-2)(x-1) = 0
⇒ y-2 = 0 ⇒ y=2
sau
⇒ x-1 =0 ⇒ x=1
b) xy -2x -y = -5
xy-2x -y +5 =0
xy -2x -y +2 +3 =0
x(y-2)- (y-2) = -3
(y-2) (x-1) = -3
↓ ↓
(-1) × 3
3 × (-1)
⇒1) y-2 = -1 ⇒y = 1
x-1 = 3 ⇒ x=4
2) y-2 =3 ⇒ y= 5
x-1 = -1 ⇒ x =0