There are several ways of doing this. I've attached a workbook to demonstrate a couple of approaches. The first uses a non-Cartesian plot and, while simple to produce, probably isn't quite as useful.
The second approach uses a table calculation and a few other tricks to get to a solution. I've attached a workbook with a tab for each approach (and scratch work). I've also included a diagram to point out a few important points. I'd be happy to answer any questions you might have!
More Complex (Scratch Work):