We can determine if the graph shows a function by using the vertical line test.
If we draw a vertical line and there are 2 or more points on that line than the graph is not a function. This is because each x value has one corresponding y value. If an x value has more corresponds to more than one y value than the relation is not a function.
If we were to draw a vertical line at x = 5, 2 points would be one that line meaning that the x value 5 corresponds to more than 1 y value, therefore the graph does not show a function.
