Relation 1:
It is a function because one point of its range (axis y) have two points in the domain (axis x).
Relation 2:
It is not a function because one point in the domain have two points in the range:
Relation 3:
It is a function because each point in the domain have a different point in the range.
Relation 4:
It is not a function because the point -7 in the domain have three values for the range:
The answer is, the relations: 2,4 are not functions and the functions 1, 3 are functions.
