2. 1/(х - 3) - 6/(x^2 - 9) = 1/(x - 3) - 6 /(x + 3)(x - 3) = ((x + 3) - 6)/(x + 3)(x - 3) =
(x + 3 - 6) / (x + 3)(x - 3) = (x - 3) /(x + 3)(x - 3) = 1 /(x + 3)
3. (a - 4) /(a^2 + 4a + 16) + 12a / (a^3 - 64) - 1 / (a - 4) = (a - 4) / (a^2 + 4a + 16) + 12a / ((a - 4)(a^2 + 4a + 16)) - 1/(a - 4) = ((a -4)(a - 4) + 12a - (a^2 + 4a + 16)) / ((a - 4)(a^2 + 4a + 16)) = (a^2 - 8a + 16 + 12a - a^2 - 4a - 16) / ((a - 4)(a^2 + 4a + 16)) = 0 / (a^3 + 64) = 0