Giải phương trình: a) (x - 3)(x + 3) - (x + 5)(x - 1) = 6; b) (3x - 2)^2 - (2x + 1)^2 - (5x - 1)(x + 1) = 20

a) (x - 3)(x + 3) - (x + 5)(x - 1) = 6
b) (3x - 2)^2 - (2x + 1)^2 - (5x - 1)(x + 1) = 20
c) (2x + 1)(4x^2 - 2x + 1) + (3 - 2x)(9 + 6x + 4x^2) + 12x = 4