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

(x² - 5x + 7)(x² + 5x + 7)

(x² - 5x + 7)(x² + 5x + 7)

Rearranging the above terms, we get,

[(x² + 7) - 5x][(x² + 7) + 5x]

We know that

a² - b² = (a - b)(a + b).

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

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