Which products result in a difference of squares or a perfect square trinomial? Check all that apply.
(5x + 3)(5x – 3)
(7x + 4)(7x + 4)
(2x + 1)(x + 2)
(4x – 6)(x + 8)
(x – 9)(x – 9)
(–3x – 6)(–3x + 6)