Which graph shows a set of ordered pairs that represents a function?

There is a rule for functions:

One input(x-value) can only have one output(y-value).

If one input has more than one output, it is not a function.

(This doesn't apply to outputs, one output can have more than one input and still be a function)

This graph shows a set of ordered pairs that does NOT represent a function because there are two points on x = -3. The input -3 has more than one output of -4 and 4, so it is not a function.

explanation:

previous steps have made pa≅ pb ≅ st ≅ su. setting the compass width to ab allows you to make tu the same length. then δstu ≅ δpab by the sss congruence postulate, and ∠p ≅ ∠s by the reason cpctc.