Х² - (3Х+7)² = (Х - (3Х+7))(Х + (3Х+7)) = (Х - 3Х - 7)(Х + 3Х + 7) = (-2Х - 7)(4Х + 7) = -(2Х + 7)(4Х + 7)
Х² - (3Х+7)² = (Х - (3Х+7))(Х + (3Х+7)) = (Х - 3Х - 7)(Х + 3Х + 7) = (-2Х - 7)(4Х + 7) = -(2Х + 7)(4Х + 7)