Answer
There are no absolute extreme values.
Work Step by Step
Note that the graph approaches, but never reaches the points $(0,-1)$ and $(0,1)$.
(These points are NOT on the graph.)
We can not find a point on the graph such that its y-coordinate is greater than any other y-coordinate on the graph.
Whichever x we choose in the (left) vicinity of $x=0,\ \displaystyle \frac{x}{2}$ is closer to 0, and
the value of $f(\displaystyle \frac{x}{2})$ will be greater than $f(x)$.
Thus, there are no absolute maxima.
Similarly, we can not find a point on the graph such that its y-coordinate is smaller than any other y-coordinate.
Whichever x we choose in the (right) vicinity of $x=0$, the value of $f(\displaystyle \frac{x}{2})$ will be smaller than $f(x)$.
Thus, there are no absolute minima.
