Answer the questions for the function f(x) = 4x4 - 48x³ a. Find formulas for f'(x) and f''(x). f'(x) = 16x³ - 144x² f''(x) = 48x² - 288x Enter f(x), f'(x), and f''(x) into your grapher to examine the table. b. Set f'(x) = 0 to find the critical numbers. One of the critical numbers of f(x) is x = 0. What is the other critical number? X = 9 What is true about f(x) at this positive critical number? Select the correct choice below and, if necessary, fill in the answer boxes within your choice. A. The graph of f is concave up and f has a relative maximum at B. The graph of f is concave up and f has a relative minimum at C. The graph of f is concave down and f has a relative maximum at ( D. The graph of f is concave down and f has a relative minimum at ( E. No conclusion can be made.