21x^2 - 6x - 3 - 2x^2 + 13x + 15 = 21−221 - 221−2x^2 + −6+13-6 + 13−6+13x + −3+15-3 + 15−3+15 = 19x^2 + 7x + 12
21x^2 - 6x - 3 - 2x^2 + 13x + 15 = 21−221 - 221−2x^2 + −6+13-6 + 13−6+13x + −3+15-3 + 15−3+15 = 19x^2 + 7x + 12