(5x - 7y)(5x + 7y) + (7x - 5y)(7x + 5y) = (5x)² - (7y)² + (7x)² - (5y)² =
= 25x² - 49y² + 49x² - 25y² = 74x² - 74y²
(5x - 7y)(5x + 7y) + (7x - 5y)(7x + 5y) = (5x)² - (7y)² + (7x)² - (5y)² =
= 25x² - 49y² + 49x² - 25y² = 74x² - 74y²