Question

x^3 - 4x^2 - 12x + 27

Answer 1

x^3+3x^2-7x^2-21x+9x+27=0

x^2(x+3)-7x(x+3)+9(x+3)=0

(x+3)(x^2-7x+9)=0

x = -3 hoặc x^2 - 7x + 9 = 0 (chuyển về pt dạng kx^2 + m)

Bạn chuyển 7x = 2 . x . 7/2 + 49/4 - 49/4

Answer 2

=x^3 +3x^2 - 7x^2 - 21x +9x + 27 

=x^2(x+3)-7x(x+3)+9(x+3) 

=(x+3)(x^2-7x+9)