I truly like visual aides when it comes to geometry.
I also found some really good uses for cosine curves to manage tangency.
Put the two together and you get a need to visualize what is really going on when you see a cos() function in a sketch, datum curve, or graph.
Well, I put it together in a little part file that lets you see what cos(n) returns.
For instance, a trajpar of cos(trajpar*360) is simply a trajpar value of 0 to 1 multiplied by 360 to return an offset from 0 throughout the curve. But what many forget is that this returns values between 1 and -1. Just pretend that the entire length of the curve is the trajpar's 0 on the start end and 1 on the finish end regardless of how long it is.
Okay, so this is basic math, but again, it is good to see math applied. And there's nothing like dynamic interaction. I attached the Creo 2.0 part file for your use.
And the bonus "pointer" is the curve's normal direction. Feel free to get some data from that if you like.
It is not perfect. It will blow the relation and if you edit the annotation, you will have to regen to get the right value. But if drag any of the 3 handles, or edit the dimension directly, the annotation will regen automatically.
I wanted to keep the sketch light enough not to be too obtrusive when editing it. If someone can figure out how to keep the vertical bar to the right of the circle, please enlighten me.
If you like this, please Like and rate this document. Thanks!
As always; comments welcome 
Creo 2.0 part file attached
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