Ta có: A(x) - C(x) = B(x), suy ra C(x) = A(x) - B(x)
a) $C(x)=(x^{3}+x^{2}+x-2)-(9-2x+11x^{3}+x^{4})$
= $x^{3}+x^{2}+x-2-9+2x-11x^{3}-x^{4}=-x^{4}-10x^{3}+x^{2}+3x-11$
b) $C(x)=(-12x^{5}+2x^{3}-2)-(9-2x-11x^{2}+2x^{3}-11x^{5})$
= $-12x^{5}+2x^{3}-2-9+2x+11x^{2}-2x^{3}+11x^{5}=-x^{5}+11x^{2}+2x-11$