(2x - 5)³ - 2x(2x - 1)(2x + 1) = 8x³ - 60x² + 150x - 125 - 2x(4x ² - 1) = 8x³ - 60x² + 150x - 125 - 8x³ + 2x = -60x² + 152x - 125
27a²(a + b) - (2a + b)³ = 27a³ + 27a²b - (8a³ + 12a²b + 6ab² + b³) = 27a³ + 27a²b - 8a³ - 12a²b - 6ab² - b³ = 19a³ + 15a²b - 6ab² - b³