Rearrange your table so that the smallest x comes first (goes on the first line) and the largest last (goes on the last line). Identify the smallest x-value. Here it seems as tho that value is 0. The "initial value" of the function is the y-value corresponding to that "initial value."
In your table, '0' shows up twice as the x-value. Thus, there is more than one y-value associated with the x-value '0.' If that's the case, we must conclude that this table does not represent a function.
