Question

(x + 2)(x² - x + 2)=0

Answer 1

(x + 2)(x² - x + 2)=0

Th1:

x + 2 = 0

x = - 2

Th2:

x² - x + 2 = 0

x² - 2 . x . 1/2 + 1/4 + 7/4 = 0

(x - 1/2)² + 7/4 = 0

(x - 1/2)² lớn hơn hoặc bằng 0

(x - 1/2)² + 7/4 lớn hơn hoặc bằng 7/4 > 0

=> loại

Vậy x = - 2

Answer 2

Ta có : 

\(\left(x+2\right)\left(x^2-x+2\right)=0\)

\(\left(x+2\right).\left[\left(x^2-2.\frac{1}{2}x+\frac{1}{4}\right)+\frac{7}{4}\right]=0\)

\(\left(x+2\right)\left[\left(x-\frac{1}{2}\right)^2+\frac{7}{4}\right]=0\)

Mà :\(\left(x-\frac{1}{2}\right)^2\ge0\)

\(\Rightarrow\left(x-\frac{1}{2}\right)^2+\frac{7}{4}\ge\frac{7}{4}\)

\(\Rightarrow\left(x-\frac{1}{2}\right)^2+\frac{7}{4}>0\)

\(\Rightarrow x+2=0\)

\(\Rightarrow x=-2\)