Which of the following must be true for an expression to be a difference of two squares?

a. both coefficients are perfect squares
b. there are only two terms
c. one term has a negative coefficient and one term has a positive coefficient

a.) a and c
b.) a, b, and c
c.) a and b
d.) b and c

A classic example of a difference of squares equation: 
x^2 - y^2

This equation consists of two perfect squares, x^2 and y^2. It also has 2 terms. We can factor this equation like this: (x-y)(x+y). If there were more than two terms, it would look different.
Also, the equation x^2+ y^2 is unfactorable.  "Difference" means something minus another thing. Therefore, one term has to have a plus sign and one term has to have a minus sign.

In your question, we have determined that A, B, and C are all true, so the letter answer is B.

A,b,and c are the anwsers