Let f (x) = x3 - x. In Examples 3 and 7 in Section 2.7, we showed that f'(x) = 3x2 - 1 and f"(x) = 6x. Use these facts to find the following. (a). The intervals on which f is increasing or decreasing. (b). The intervals on which f is concave upward or downward. (c). The inflection point of f.