Can there be an inflection point when the third derivative equals 0? My critical point from the second derivative is x = 0. To check whether there is an inflection point, I plugged it into the 3rd derivative. If it is below or above 0, there is an inflection point. Mine is EQUAL to 0. Does this mean there is a possibility my inflection point is at (0, 0) or is it undefined? How do I check?