Which relations are functions and which are not functions?
column a column b
1.
{(3, 2), (6, 4), (9, 6),
(12, 8)}
2.
{(2, 3), (2, 5), (3, 6),
(9, 4)}
3.
{(4, 2), (6, 3), (4, 8),
(6, 6)}
4.
{(3, 4), (5, 2), (6, 8),
(6, 4)}

a.
function
b.
not a function

If the x value is repeated is is not a function. (unless it is a negative and a positive)
So lets see:
For A we have 3 6 9 12 no repeations so therefore It is A
For B we have 2 2 3 9, 2 is repeated so therefore it is B
For C we have 4 6 4 6, both 4 and 6 were repeated so therefore is is B
and lastly for D we have 3 5 6 6
And 6 was repeated so therefore it is B.
A)A
B)B
C)B
D)B