а) (x-5)(x+5) = x^2 + 5x - 5x - 25 = x^2 - 25
б) (7c+3)(7c-3) = 49c^2 - 9
в) (4x-9y)(4x+9y) = 16x^2 - 36y^2
г) (a^2-2b)(a^2+2b) = a^4 - 4b^2
а) (x-5)(x+5) = x^2 + 5x - 5x - 25 = x^2 - 25
б) (7c+3)(7c-3) = 49c^2 - 9
в) (4x-9y)(4x+9y) = 16x^2 - 36y^2
г) (a^2-2b)(a^2+2b) = a^4 - 4b^2