In order for the order pairs to be a function. All of the x coordinates must be different from each other, they can't be the same. There can't be any repeats of the x coordinates. But for the y coordinates, it's okay for them to be the same. The reason why you would eliminate (-1,5) is because there are 2 -1 x coordinates, and that would not make the ordered pairs a function. When you remove them, none of the x coordinates are the same anymore, so it would now be a function.
