The curve is not a function of $x$.
Work Step by Step
RECALL: The Vertical Line Test states that if all vertical lines will pass through a graph in at most one point, then the graph represents a function of $x$. Note that most vertical lines (e.g., $x=0$, $x=-1$, $x=1$, etc.) that will pass through the graph at two different points. The graph fails the vertical line test. Thus, the curve does not represent a function of $x$.