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 - 5x)² - 7²

Hence, (x² - 5x + 7)(x² - 5x - 7) = (x² - 5x)² - 7².