(-1,-2) would result in a relation that is no longer a function.
In the table, there's already x = -1 and y = -4. Function only gives a single y-value with x-value. If a single x-value gives two y-values then it'd not be Function.
If we add (-1,-2) in the table. The domain will be repetitive. Basically, we already have (-1,-4) and if we add (-1,-2) in the table, a single x-value will give TWO y-values which is not a function.