Find the intervals on which​ f(x) is​ increasing, the intervals on which​ f(x) is​ decreasing, and the local extrema.   ​f(x)=2x4 +8x3+33 Question content area Part 1 Refer to the previous problem. Provide the following answers in the text field below.   ​(a) Identify the first derivative f​ '(x).   ​(b) Identify all partition values.   ​(c) Evaluate the first derivative at all relevant test values. To save​ time, do not show work. Simply give the test value and its function value.