Answer:
All of the examples define relations between a domain and range.
Such a relation will be a function if and only if each value in the domain corresponds to at most one value in the range.
In the first example, the value
−
1
in the domain is associated with two values in the range, namely
−
5
and
1
.
In the second example, the value
−
1
in the domain is associated with two values in the range, namely
7
and
1
.
In the third example, the value
3
in the domain is associated with two values in the range, namely
2
and
4
.
In the fourth example, each of the values in the domain is associated with one value in the range, so this describes a function. Note however that the values
−
4
and
−
7
are both mapped to
5
. So the function described is not one to one and consequently its inverse is not a function.