A difference in squares is a polynomial expression written in the identity of *Note that it is not possible to factor a sum of squares like i.e. . It is not possible to find two integers whose product is positive and whose sum is 0.*

In the identity , we can replace a and/or b by numbers, variables, monomials and polynomials. For example, can be written and can be factored using the above identity with ; . This factoring can be verified by expanding the product of the factors.