How to find amplitude on diagonal curve?

Hello all,

I have a data set that consists of a roughly sinusoidal curve in a coordinate plane. I am trying to find the amplitude, wavelength and frequency of the data, which would be easy but for one thing: the linear trendline through the curve is sloped upward. Ideally, I would like to "rotate" the curve so that the trendline is parallel to the x-axis, because this would make it easy to calculate my desired variables. Any ideas? I can post a sample if it would help my explanation. Thanks in advance.

Example.xlsx

Column A is a time point, B is x coordinates, and C is y coordinates. I plotted a scatterplot of x vs. y to show what the data looks like currently.

Originally Posted by shg

See attached. I used Solver to get the rotation angle. It could be done in closed form, but I didn't want to think that hard.

That is exactly what I need. I have never used Solver though; how do I get the rotation angle using it? Thanks a lot! You are a life (and thesis) saver.

Sorry, I still don't follow that step. The model shows a angle of -.837, but there is no formula shown in that cell and I can't figure out how you got there. I can open Solver, but I'm not sure what values to input and where to get that angle number. I tried copying what was shown when I open solver in your model but it gives me an error message.