PolynomialExtendedGCD

PolynomialExtendedGCD[poly1,poly2,x]
gives the extended GCD of and treated as univariate polynomials in x.

PolynomialExtendedGCD[poly1,poly2,x,Modulusp]
gives the extended GCD over the integers mod prime p.

Introduced in 2007
(6.0)