First and second relations
We can use the vertical line test. It consists of drawing any vertical line on the graph of the relation.
• If the line passes through two points or more, the relation is not a function.
,
• If the line passes only through one point, the relation is a function.
Graphically,
First relation
Since the line passes only through one point, then this relation is a function.
Second relation
Since the line passes through two points, then this relation is not a function.
Third relation
On the other hand, a relation is a function if the x-values map to only one y-value.
In this case, we can see that there are two different values of y when x = 2, that is:

Since the x-values do not map to only one y-value, this relation is not a function.
Fourth relation
Again, a relation is a function if the x-values map to only one y-value. In this case, we can see that each element of the set of x-values connects one by one with elements of the set of y-values.
Therefore, this relation is a function.
Fifth relation
In this case, we can see that there are two different values of y when x = -5, that is:

Since the x values do not map to only one y-value, this relation is not a function.
Sixth relation
In this case, we can see that there are two different values of y when x = -4, that is:

Since the x values do not map to only one y-value, this relation is not a function.
In summary, we have:
• First relation: Is a function.
,
• Second relation: Is not a function.
,
• Third relation: Is not a function.
,
• Fourth relation: Is not a function.
,
• Fifth relation: Is not a function.
,
• Sixth relation: Is not a function.