Explanation 1)A vertical line can be represented by the equation x=a, where a can be any number. If you think about it, there is no y in the function, this making it not a function.
Explanation 2) For a line to be a function it has to pass the vertical line test, so you will draw a vertical line through the function and if it touches more than one point then it is not a function. In this case if you draw a vertical line through a vertical line there are an infinite number of places where the lines intercept, so it is not a function.
In mathematics, the vertical line test is a visual way to determine if a curve is a graph of a function or not. A function can only have one output, y, for each unique input, x. ... If the vertical line you drew intersects the graph more than once for any value of x then the graph is not the graph of a function.
