Is the derivative of function f (x) = [(4 + x ^ 2) ^ (1 / 2)] / 2 + (6-x) / 6 calculated by power law or by chain rule? How to choose the derivative formula?

Is the derivative of function f (x) = [(4 + x ^ 2) ^ (1 / 2)] / 2 + (6-x) / 6 calculated by power law or by chain rule? How to choose the derivative formula?

F (x) = [1 / 2 * (4 + x ^ 2) ^ (- 1 / 2) * (2 * x)] / 2 + (- 1) / 6 = x / [2 (x ^ 2 + 4) ^ (- 1 / 2)] - 1 / 6