Question 592852
why isn't (1,3) (2,2) (1,5) (2,6) a function
For an expression to be a function, for each x there must only be only one y. 
You will note that for points (1,3) and (1,5), x has two different values y. 
Similarly, (2,2 and (2,6) show the same. Therefore, these points are not from a function.
If you graph these points, you will get a curve similar to a parabola opening rightwards and it would fail the vertical line test which allows only one intersection for a function.