To determine whether these points are local maximas, minimas, or neither, we need to consider the intervals between each of the points. Plug in a value from each interval into the first derivative of the function. If the value is positive, then that is an interval of increase. If the value is negative, then that is an interval of decrease. Finally, if two neighboring intervals change sign then that point is either a local maxima or minima. If the first interval is positive and the second interval negative, then the critical point is a local maxima. If the first interval is negative and the second interval positive, then the critical point is a local minima. If both intervals are positive or both intervals are negative, then the critical point is neither a local maxima or minima.