x² - 2xy + y² - 5x + 5y - 16 = (x² - 2xy + y²) - (5x - 5y) - 16 =
= (x - y)² - 5(x - y) - 16 = 9² - 5 * 9 - 16 = 81 - 45 - 16 = 20
x² - 2xy + y² - 5x + 5y - 16 = (x² - 2xy + y²) - (5x - 5y) - 16 =
= (x - y)² - 5(x - y) - 16 = 9² - 5 * 9 - 16 = 81 - 45 - 16 = 20