(6x2 – 5x + 9) – (3x2 + x - 7) = 6x2 – 5x + 9 – 3x2 – x + 7 = (6x2 - 3x2) + (-5x - x) + (9 + 7) = 3x2 - 6x + 16
Ответ: 3x2 - 6x + 16