Consider the following. (If an answer does not exist, enter DNE.) f' (x ) = 4x2 - 1 (a) Find the open intervals on which f'(x) is increasing or decreasing. (Enter your answers using interv increasing decreasing (b) Find the open intervals on which the graph of f is concave upward or concave downward. (Enter you concave upward concave downward (c) Find the x-values of the relative extrema of f. (Enter your answers as a comma-separated list.) relative maximum X = relative minimum X : Find the x-values of the inflection points of f. (Enter your answers as a comma-separated list.) X =