(9-а)(9+а) = 9² - а² = 81 - а²
(3b-1)(3b+1) = (3b)² - 1² = 9b² - 1
(x+7)(7-x) = 7² - x² = 49 - x²
(4a-b)(b+4а) = (4a)² - b² = 16а² - b²
(6x-2)(6x+2) = (6x)² - 2² = 36x² - 4
(3x-5y)(3x+5y) = (3x)² - (5y)² = 9x² - 25y²
(8m-9n)(8m+9n) = (8m)² - (9n)² = 64m² - 81n²
(2c-3a²)(3a²+2c) = (2c)² - (3a²)² = 4c² - 9
69·71 = (70-1)·(70+1) = 70² - 1² = 4900-1 = 4899
58·62 = (60-2)·(60+2) = 60² - 2² = 3600-4 = 3596