P(x) = (x^{2} - 2x - 1)(2x - 1) - 4

P(x) = 2x(x^{2} - 2x - 1) - x^{2} + 2x + 1 - 4

P(x) = 2x^{3} - 4x^{2} - 2x - x^{2} + 2x + 1 - 4