(x + 2). (x² - 2x + 4) -x (x+2). (x - 2)

(x + 2) * (x² - 2x + 4) - x * (x + 2) * (x - 2) = x³ + 2x² - 4x + 2x² - 4x + 8 - x² - 2x² + 4x = x³ - x² + 4