Its not a function. The reason its not a function is because it doesnt pass the vertical line test. You could graph these points physically or you could think about it. The domain is the x value, while the range is the allowed y values. So by having the same x value relate to two different y values, just makes no sense. Imagine the function is x+4 and we are given in that graph that when x equals 6, the y equals 9 and 10. That isnt possible because we know the answer is 10, not 9, it cant be both.
Another way you could prove this is by graphing. If you try to take the slope in that interval where 6 coorelates to two y values. The change in y is 1, but the change in x is 0. When you divide 1/0, your calculator blows up. Try it
