After factoring a trinomial into two binomials, what is the final step used to confirm the answer is correct?

1. Every worked example in this method ends with a check by multiplying the two binomial factors back together. 2. If the product of the binomials matches the original trinomial, the factoring is confirmed correct. 3. Adding, dividing, or substituting zero are different operations that do not test whether the factored form expands back to the original expression. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 7 "Factoring", section 7.2 Factor Quadratic Trinomials with Leading Coefficient 1_