Help me 1. Circle each relation that is a function.
{(1, 3), (1, 5), (2, 7), (3, 9), (4, 11)}
{(0, 0), ( 21, 21), ( 22, 22), ( 23, 23)}
{(5, 5), (5, 4), (5, 3), (5, 2)}
{(2, 5), (3, 5), (4, 5), (5, 5)}

2 and 4

Step-by-step explanation:

A relation describe a function when for every x is associated one and only one y

1) is not a function because when x = 1 there are two y associated (3 and 5)

2)  yes, for the definition of function

3) is not a function because when x = 5 there are four y associated ( 5, 4, 3, 2)

4) yes, because for every x there is only one y associated (is not important if is the same)