Help, Concaved downward?? Let f(x) = 12x^(2/3) Find all the intervals on which f(x) is concaved downward. I know I have to take the second derivative to find the inflection point to find the interval. I figured the first derivative to be (8-4x^(1/3)/x^(1/3) I can't seem to get the second derivative to work out. Please Help!