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