The way you can tell if a function is linear or non-linear is if the rate of change is constant. Here you can tell it isn't the whole time.
-3 to -1 is +2
-1 to 0 is +2
0 to 1 is +1 (Here is where the rate of change changes, making it non-linear.)
But just in case, let's check the y-values.
-5 to -1 is +4
-1 to 1 is +2 (Again, here is where you can tell)
Hope this helps!
