Consider this equation:
$$xy = 4y + 9$$
When we plot a graph of $xy$ against $y$, is the vertical intercept a defined value?
My question is because I feel that the vertical intercept should be undefined since when $y = 0$, $xy$ must be equal to $0$ given that any value multiplied by $0$ is $0$. But on my textbook, the graph drawn doesn't indicate so.
Edit: What I mean by plot XY against Y is that the term XY is the vertical axis and Y is the horizontal axis.