Which of the following relations is not a function? a. (5,4) (-1,2) (1,1) (-8,2) b. (1,4) (-1,2) (1,1) (-8,2) c. (-1,4) (1,2) (5,1) (-8,5) d. (-8,4) (1,3) (-1,1) (5,2)

According to Wikipedia: "In mathematics, a function is a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output."

So based of this we need to look for a set where one of the x values or the y values is the same, and the other number is different.

B.
(1,4) and (1,1) both have the same x, but different y!