\[\boxed{\text{870.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (x - y)(x + y) = x² - y²\]
\[\textbf{б)}\ (p + q)(p - q) = p² - q²\]
\[\textbf{в)}\ (p - 5)(p + 5) = p² - 25\]
\[\textbf{г)}\ (x + 3)(x - 3) = x² - 9\]
\[\textbf{д)}\ (2x - 1)(2x + 1) = 4x² - 1\]
\[\textbf{е)}\ (7 + 3y)(3y - 7) = 9y² - 49\]
\[\textbf{ж)}\ (n - 3m)(n + 3m) = n² - 9m²\]
\[\textbf{з)}\ (2a - 3b)(2a + 3b) = 4a² - 9b²\]
\[\textbf{и)}\ (8c + 9d)(9d - 8c) = 81d² - 64c²\]