A function can be either be a one-to-one OR many-to-one.
In the coordinates (x,y) map out each x to a different diagram, and y another diagram.
The x's are ( 3, 2, 8, 1, 2 ), and the y's are ( 5, 1, 7, 1, 7 )
As shown in the diagram above. the x element 2 exhibits a one-to-many relation (2,1) and (2,7), therefore, these sets of ordered pairs is NOT a function.