Answer
We use the graph below as an example of demonstration. The curve is symmetric around the x-axis and is not $ y=0$. If we draw a vertical line, there will be two points on the curve with coordinates $ P_{1}(x,y_{1})$ and $ P_{2}(x,-y_{1})$.
We see that unless $ y_{1}=0$, the curve can not be a graph of a function (which requires a single intersection on the graph for each x-value).
Work Step by Step
Given above.
