Answer the following questions about the function whose derivative is given below. a. What are the critical points of f? b. On what open intervals is f increasing or decreasing? c. At what points, if any, does f assume local maximum and minimum values? f' (x) = (6 sin x - 6) (2 cos x + 13 ) , OSXS 2x . . . a. What are the critical points of f? X = (Use a comma to separate answers as needed.)