1) (x + 2)(x - 5) - 3x(1 - 2x) = x² + 2x - 5x - 10 - 3x + 6x² = 7x² - 6x - 10
2) (a + 3)(a - 2) + (a - 3)(a + 6) = a² + 3a - 2a - 6 + a² - 3a + 6a - 18 = 2a² + 4a - 24 = 2(a² + 2a - 12)
3) (x - 7)(3x - 2) - (5x + 1)(2x - 4)= 3x² - 21x - 2x + 14 - (10x² + 2x - 20x - 4) = 3x² - 23x + 14 - 10x² + 18x + 4 = -7x² - 5x + 18