(-x + 5)(x + 5) = - (x - 5)(x + 5) = - (x² - 25 ) = 25 - x²
(- 10 + 6b)(- 10 - 6b) = -(6b - 10)(6b + 10) = - ( 36b² - 100) = 100 - 36b²
(8l + 5)(- 10 + 16l) = - 2(8l + 5)(5 - 8l) = - 2 (25 - 64l²) = 128l² - 50
(21s - 12)(8 + 14s) = 3 * 2 *(7s - 4)(4 + 7s) = 6(49s² - 16) = 294s² - 96