The following are the answers for these:
(5x + 3)(5x – 3) ----> Difference of squares
(7x + 4)(7x + 4) ----> Perfect square trinomial
(2x + 1)(x + 2) ----> Neither
(4x – 6)(x + 8) ----> Neither
(x – 9)(x – 9)-----> Perfect square trinomial
(–3x – 6)(–3x + 6) -----> Difference of squares.
The easiest way to tell these is that if the parenthesis are exactly the same it will be a perfect square trinomial. If the parenthesis are the same except for the sign in between the terms, it is a difference of square. If it has neither of these, then it is neither.
