=x2[x-3]-4[x-3]
=[x2-4][x-3]
=[x-2][x+2][x-3]
x3 - 3x2 - 4x + 12
= (x3 - 3x2) - (4x - 12)
= x2 (x - 3) - 4 (x -3)
= (x2 - 4) (x - 3)
= (x + 2) ( x - 2) (x - 3)
Cách khác:
\(x^3-3x^2-4x+12\)
\(=\left(x^3-4x\right)-\left(3x^2-12\right)\)
\(=x.\left(x^2-4\right)-3.\left(x^2-4\right)\)
\(=\left(x^2-4\right).\left(x-3\right)\)
\(=\left(x^2-2^2\right).\left(x-3\right)\)
\(=\left(x-2\right).\left(x+2\right).\left(x-3\right)\)
Chúc bạn học tốt!