Determining if a graph is a function of x
We know a function is determined by the following condition:
each value of x (input) has one value of y (output) related.
Using the vertices line test we have that there are not inputs with more than one output.
But there are x values with no y values related, then this is a function but this is not a function of x, because there are x values with no output.
Answer: y is not a function of x, it is a function of a subset of x
