Explanation:
the range is the interval or set of all valid y (functional result) values.
we see that y goes continuously through every value between +5 (we see no y values bigger than that) and -5 (we see no y values lower than that).
the filled dots also tell us that the end points would be included (if this would be a necessary information - it is not, because the curve reaches +5 and -5 also in between).
so, the range is
-5 <= y <= +5