Bonjour,
3(4x + 7) + 4(2x - 9) = 3 * 4x + 3 * 7 + 4 * 2x + 4 * -9 = 12x + 21 + 8x - 36 = 20x - 15
7x(2x - 5) - x(2x - 5) = 7x * 2x + 7x * -5 - x * 2x - x * -5 = 14x² - 35x - 2x^3 + 5x = - 2x^3 + 14x² - 30x.
(2x + 5)(3x + 7) = 2x * 3x + 2x * 7 + 5 * 3x + 5 * 7 = .......
(2x - 5)(3x - 2) = 2x * 3x + 2x * -2 - 5 * 3x - 5 * -2 = ......
