Express each of the following as the difference of two squares:

(x² + 5x - 7)(x² - 5x + 7)

(x² + 5x - 7)(x² - 5x + 7) = [{x² + (5x - 7)}{x² - (5x - 7)}]

As, we know that,

a² - b² = (a - b)(a + b).

∴ [{x² + (5x - 7)}{x² - (5x - 7)}] = (x²)² - (5x - 7)².

Hence, (x² + 5x - 7)(x² - 5x + 7) = (x²)² - (5x - 7)².