will be increasing on the intervals where and decreasing wherever . Local extrema occur when and the sign of changes to either side of that point.
is positive when is between -4 and some number between -2 and -1, and also 2 (exclusive) and 4, so you can estimate that is increasing on the intervals [-4, -2] and (2, 4].
is negative when is between some number between -2 and -1, up to some number less than 2. So is decreasing on the interval [-1, 1].
You then have two possible cases for extrema occurring. The sign of changes for some between -2 and -1, and again to either side of .