Chapter P - Section P.4 - Polynomials - Exercise Set - Page 57: 100

See explanations.

Let $A, B$ be the two terms. The sum is $A+B$. The difference is $A-B$. Their product is given by $(A+B)(A-B)=A^2-B^2$, that is the difference of their squares. For example, $A=2x, B=3y$, $(2x+3y)(2x-3y)=4x^2-9y^2$