Let f(z) x - 8x2 3 (a) Use the definition of a derivative or the derivative rules to find f'(x) = (b) Use the definition of a derivative or the derivative rules to find f''(x) = (c) On what interval is f increasing (include the endpoints in the interval)? interval = (d) On what interval is f decreasing (include the endpoints in the interval)? interval = (e) On what interval is f concave downward (include the endpoints in the interval)? interval = (f) On what interval is f concave upward (include the endpoints in the interval)? interval =