PolynomialRemainder

PolynomialRemainder[p, q, x] gives the remainder from dividing p by q, treated as polynomials in x.

Examples

Get remainder after division:

PolynomialRemainder[x^3 + 2x^2 + x + 1, x + 1, x]
(* 1 *)

Another example:

PolynomialRemainder[x^4 + x^2, x^2 + x + 1, x]
(* 1 + x *)

Please visit the official Wolfram Language Reference for more details.