(5x + y)² - (x - 5y)² = (5x + y - x + 5y)(5x + y + x - 5y) =
= (4x + 6y)(6x - 4y) = 2 * (2x + 3y) * 2 * (3x - 2y) = 4(2x + 3y)(3x - 2y)
(5x + y)² - (x - 5y)² = (5x + y - x + 5y)(5x + y + x - 5y) =
= (4x + 6y)(6x - 4y) = 2 * (2x + 3y) * 2 * (3x - 2y) = 4(2x + 3y)(3x - 2y)