a) (x + 1)^2 = x + 1
=> (x + 1)^2 - (x + 1) = 0
=> (x + 1)(x + 1 - 1) = 0
=> x(x + 1) = 0
=> x = 0
Hoặc x + 1 = 0
=> x = 0 - 1 = -1
Vậy x = 0 hoặc x = -1.
b) (x + 8)^2 = 121
TH1, (x + 8)^2 = 11^2
=> x + 8 = 11
=> x = 11 - 8
=> x = 3
TH2, (x + 8)^2 = (-11)^2
=> x + 8 = -11
=> x = -11 - 8
=> x = -19
Vậy x = 3 hoặc x = -19.
c) x^2 + 8x + 16 = 0
=> x^2 + 2.x.4 + 4^2 = 0
=> (x + 4)^2 = 0
=> x + 4 = 0
=> x = 0 - 4
=> x = -4
Vậy x = -4.
d) 4x^2 - 12x = -9
=> 4x^2 - 12x + 9 = 0
=> (2x)^2 - 2.2x.3 + 3^2 = 0
=> (2x - 3)^2 = 0
=> 2x - 3 = 0
=> 2x = 0 + 3
=> 2x = 3
=> x = 3/2
Vậy x = 3/2.
@vietdorapan
