Explain why the product of two binomials in the form (a+b) (a-b) is a binomial instead of a trinomial

According to notable products, when you have to multiply the sum of a binomial (a+b) times the difference of itself (a-b), the result is the difference between the terms of the binomial to the power of 2 (a^2 - b^2)

Step-by-step explanation:

The reason for this is that the two middle terms, ba and - ba, cancel one another out, leaving only two terms: a^2 and b^2.