Hi all. What does it mean that a function in polar coordinates may not be a function in Cartesian coordinates? For example, [itex] r(\theta) = 1 + \sin\theta [/itex] is a function because each [itex]\theta[/itex] corresponds to a single value of [itex]r[/itex]. However, in Cartesian coordinates, the graph of this function most clearly fails the vertical line test. Therefore, functionality depends on the coordinate system?