Table 1
Input (x)               1            3           5            5              9
Output (y)             7           16          19          20           28
We know that a function is a relation where each input or x-value of the X set has a unique y-value or output of the Y set.
In other words, we can not have duplicated inputs as there should be only 1 output for each input.
From Table 1, it is clear that:
- Each input or x-value of the X set has a unique y-value or output of the Y set.
- There is no duplicated input (repeated x value).
Therefore, Table 1 represents a function.
                                                 Table 2
Input (x)               0.5          7           7            12            15
Output (y)             7           15          10          23           30
  
We already know that a function is a relation where each input or x-value of the X set has a unique y-value or output of the Y set.
In other words, we can not have duplicated inputs as there should be only 1 output for each input.
From Table 2, it is clear that:
- There is a duplicated input (repeated x value) i.e. x = 7 appears twice. And we can not have repeated input values.
As the input x = 7 is repeated multiple times, thus, the given table 2 does not represent a function.
Therefore,  Table 2 does not represent a function.