A) (a-c)(a+c) - (a- 2c)^2 = a^2 - c^2 - a^2 + 4ac - 4c^2 = 3ac - 3c^2
б)(x-4)(x+4) - (x-8)(x+8) = x^2 - 16 - x^2 + 64 = 48
в)(3b-1)(3b+1) - (b-5)(b+5) = 9b^2 - 1 - b^2 + 25 = 8b^2 +24
г)(m+ 3n)^2 + (m +3n)(m-3n) = m^2 +6nm + 9n^2 + m^2 - 9n^2 = 2m^2 + 6nm