Simplify:

(px - q) (px + q)

(px - q) (px + q)

= px (px + q) - q (px + q)

= p⁽¹⁺¹⁾x⁽¹⁺¹⁾ + pqx - pqx - q⁽¹⁺¹⁾

= p²x² + pqx - pqx - q²

= p²x² - q²

Hence, (px - q) (px + q) = p²x² - q²