It is not a function because an x-value can only have 1 y-value (but a y-value can have as many x-values as it wants. For example, [(2,5),(2,7),(4,6),(8,9)] is not a function because the x-value “2” has multiple y-values but [(5,7),(6,7),(2,7),(8,6)] is a function because each x-value has just one y-value even though the y-value of “7” has multiple x-values.