xy (x + y) - (x² + y²) (2x - y)
= xy x + xy y - (2x x² - x² y - 2x y² + y² y)
= x²y + xy² - 2x³ + x²y + 2xy² - y³
= 2x²y + 3xy² - 2x³ - y³.
xy (x + y) - (x² + y²) (2x - y)
= xy x + xy y - (2x x² - x² y - 2x y² + y² y)
= x²y + xy² - 2x³ + x²y + 2xy² - y³
= 2x²y + 3xy² - 2x³ - y³.