Let f be the function defined as follows. y = f(x) = v9x + 8 (a) Find the differential of f. 9 dy = 2V 9x + 8 X (b) Use your result from part (a) to find the approximate change in y if x changes from 4 to 4.1 (Round your answer to three decimal places dy = (c) Find the actual change in y if x changes from 4 to 4.1 and compare your result with that obtained in part (b). (Round your answer to thre decimal places.) Ay =