2.10. Rút gọn: a) (x+1)^3-(x-1)^3-6(x-2)(x+2) b) (x-y)^3+(x+y)^3+(y-x)^3-3xy(x+y)

a) Expanding and simplifying:(x³ + 3x² + 3x + 1) - (x³ - 3x² + 3x - 1) - 6(x² - 4) = 6x² + 2 - 6x² + 24 = 26b) Let A = x - y, B = x + y, C = y - x = -A. Then we have:A³ + B³ + C³ - 3xy(x+y) = A³ + B³ - A³ - 3xyB = B³ - 3xyB = B(B² - 3xy) = (x+y)((x+y)² - 3xy) = (x+y)(x² + 2xy + y² - 3xy) = (x+y)(x² - xy + y²) = x³ + y³