(3x-4)(3x+4) = 9x^2 - 12x + 12x - 16 = 9x^2 - 16
(a^2 + 2)(a^2 - 2) = a^4 - 2a^2 + 2a^2 - 4 = a^4 - 4
(3x-4)(3x+4) = 9x^2 - 12x + 12x - 16 = 9x^2 - 16
(a^2 + 2)(a^2 - 2) = a^4 - 2a^2 + 2a^2 - 4 = a^4 - 4