а) (x-5)(x+5) = x^2 + 5x - 5x - 25 = x^2 - 25
б) (3m-4n)(3m+4n) = 9m^2 - 12mn + 12mn - 16n^2 = 9m^2 - 16n^2
в) (-7x-y)(7x-y) = -49x^2 + 7xy - 7xy + y^2 = -49x^2 + y^2
а) (x-5)(x+5) = x^2 + 5x - 5x - 25 = x^2 - 25
б) (3m-4n)(3m+4n) = 9m^2 - 12mn + 12mn - 16n^2 = 9m^2 - 16n^2
в) (-7x-y)(7x-y) = -49x^2 + 7xy - 7xy + y^2 = -49x^2 + y^2