1) x^2 + 2x + 1 = x + 1
x^2 + 2x + 1 - x - 1 = 0
x^2 + x = 0
x(x+1) = 0
Vậy x = 0 hoặc x=-1
2) (4 - x) - 2 (x-4)^2 = 0
(4-x) +2.(4-x)^2 =0
(4-x) [1+2.(4-x)] = 0
(4-x) (1+8-2x) = 0
(4-x) (9-2x) = 0
Vậy x = 4
3) x(y+1) - y - 1 = 0
x(y+1) - (y+1) = 0
(y+1) (x-1) = 0
Vậy y = -1 và x = 1
4) (x^2+1)(x-2) + 2x - 4 = 0
(x^2+1)(x-2) + 2(x - 2) = 0
(x-2) (x^2+1+2) = 0
(x-2) (x^2 +3) = 0
Vậy x=2