X^4+5x^3-9x^2-81x-108
= x^4 + 3x^3 +2x^3 + 6x^2 - 15x^2 - 45x -36x -108
= (x+3)(x^3 + 2x^2 - 15x -36)
= (x + 3) (x^3 + 3x^2 - x^2 - 3x -12x - 36)
= (x + 3)^2 (x^2 - x - 12)
= (x + 3)^3(x-4)
X^4+5x^3-9x^2-81x-108
= x^4 + 3x^3 +2x^3 + 6x^2 - 15x^2 - 45x -36x -108
= (x+3)(x^3 + 2x^2 - 15x -36)
= (x + 3) (x^3 + 3x^2 - x^2 - 3x -12x - 36)
= (x + 3)^2 (x^2 - x - 12)
= (x + 3)^3(x-4)