Problems 27-40, find the intervals on which f(x) is increasing, the intervals on which f(x) is decreasing, and the local extrema.
28. f(x) = -3x2 - 12x
30. f(x) = -3x2 + 12x - 5
32. f(x) = -x3 - 4x + 8
34. f(x) = -2x3 + 3x2 + 120x
36. f(x) = x4 + 2x3 + 5
38. f(x) = x In x - x
40. f(x) = (x2 - 9)2/3