d) Tìm đa thức K(x) sao cho H(x) – K(x) = 1/2 x^2.

d) Ta có: H(x) – K(x) = 12x².

Suy ra K(x) = H(x) – 12x².

Hay K(x) = x³ – x² + x – 1 – 12x².

                = x³ + (– x² – 12x²) + x – 1

                = x³ – 32x² + x – 1.

Vậy K(x) = x³ – 32x² + x – 1.