I have this idea for a graph but don't know what function could describe it better.
The idea is something like the "squared" function turned $90$ degrees to the right, so that possible values for $x$ are always positive and $y$ may be both positive and negative.
The graphs of $\sqrt x$ and $-\sqrt x$ combined look good too, but I don't know how to write that as a single function (eh, I'm so bad with these things).
Basically, anything that may look like this will do.
Looking forward to some solution.