`f(x) = 2x^4 + x^3 - 16x^2 + 3x + 18`
`= 2x^4 + 2x^3 - x^3 - x^2 - 15x^2 - 15x + 18x + 18`
`= 2x^3(x + 1) - x^2(x + 1) - 15x(x + 1) + 18(x + 1)`
`= (2x^3 - x^2 - 15x + 18)(x + 1)`
`= (2x^3 - 4x^2 + 3x^2 - 6x - 9x + 18)(x + 1)`
`= [2x^2(x - 2) + 3x(x - 2) - 9(x - 2)](x + 1)`
`= (2x^2 + 3x - 9)(x - 2)(x + 1)`
`= (2x^2 + 6x - 3x - 9)(x - 2)(x + 1)`
`= [2x(x + 3) - 3(x + 3)](x - 2)(x + 1)`
`= (2x - 3)(x + 3)(x - 2)(x + 1)`
Phân tích đa thức `f(x)` thành nhân tử, ta được `f(x) = (2x - 3)(x + 3)(x - 2)(x + 1)`
