4. Упростите буквенное выражение. a) 3(x+7)-4x = 3x + 21- 4x = (3-4)x+21= x + 21 б) 7x54(2x - 9) = в) 5(х-3) (6x - 11) = г) x-7-3(2x - 8) = д) 6(2x + 3) -4(7x-20) =

б) 7x - 5 - 4(2x - 9) = 7x - 5 - 8x + 36 = (7x - 8x) + (-5 + 36) = -x + 31 в) 5(x - 3) - (6x - 11) = 5x - 15 - 6x + 11 = (5x - 6x) + (-15 + 11) = -x - 4 г) x - 7 - 3(2x - 8) = x - 7 - 6x + 24 = (x - 6x) + (-7 + 24) = -5x + 17 д) 6(2x + 3) - 4(7x - 20) = 12x + 18 - 28x + 80 = (12x - 28x) + (18 + 80) = -16x + 98