(2x + 1)(x - 4) = 2x^2 - 8x + x - 4 = 2x^2 - 7x - 4
(x - 3)(x + 5)(x - 3)(x - 5) = (x - 3)^2 (x - 5)(x + 5) =
= (x^2 - 6x + 9)(x^2 - 25) =
= x^2 (x^2 - 25) - 6x(x^2 - 25) + 9(x^2 - 25) =
= x^4 - 25x^2 - 6x^3 + 150x + 9x^2 - 225 =
= x^4 - 6x^3 - 16x^2 + 150x - 225