Consider the equation below. f(x) = 2x3 + 3x = 120x - (a) Find the interval(s) of increase and decrease. (b) Find the local minimum and maximum values of f. (c) Find the inflection point and the intervals on which f is concave up and concave down. Step 1 (a) Find the interval(s) of increase and decrease. For f(x) = 2x3 + 3x - 120x, we have the following f'(x) = I This factors into ])(x + C )(x-4).