
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

.