а) 12x^2 - (4x - 3)(3x + 1)
12x^2 - (4x(3x) + 4x(1) - 3(3x) - 3(1))
12x^2 - (12x^2 + 4x - 9x - 3)
12x^2 - 12x^2 - 4x + 9x + 3
5x + 3

б) (3x - 1)(3x + 1) + (3x + 1)^2
(3x)^2 - (1)^2 + 2(3x)(1) + (3x)^2 + 2(3x)(1) + (1)^2
9x^2 - 1 + 6x + 9x^2 + 6x + 1
18x^2 + 12x + 1