Hi there Mary Dominguez, So what a vertical line test down is to find out if a particular graph is a function or not. What you do is take a vertical strait line and move it right to left or left to right, depending on your preference, along the X axis. The reason this works is a function can not have an x that has 2 different y values. If we use the vertical line test on a graph with say a graph that has (2,3) and (2,4) we can use the vertical line test and see that the line hits 2 points at once which means its not a function :)
When a vertical line passes through the graph of a function, it will intersect the graph at only one point. More than one point on any given vertical line means that the same x is being paired with 2 different y's and that make the graph not a function.
The digits will be related by a factor of 10 if they are the same digit. 4099 and 5011 have the same digit in the tens and ones places. 4110 and 5909 do not.
