ℝ[x] denotes the ring of polynomials with real coefficients in a variable x. The ring is commutative and has a multiplicative identity, the constant polynomial 1. Addition is performed coefficient-wise and products are formed by
where .
Given a commutative ring R with a multiplicative identity 1, a polynomial ring R[x] may be similarly defined. Factorization may be non-standard, though; note
and that x2−1 = 0 has four roots in ℤ8. If R is an integral domain, then the formula
holds. If R is a UFD, then R[x] is a UFD. If R is a field, then R[x] is a Euclidean domain. Polynomials rings such as R[x1, x2,…, xn] in several (or infinitely many) variables may similarly be defined.