Cosine component questions

Why does the cosine component return these values for 180 degrees (via Angle Control) vs the -1 it'd return if 180 was plugged into it with a regular slider? (see picture)
Also, (if it isn't too complicated) if I know the cosine value of an angle, how do I determine the angle in degrees (with math components?)
Thanks in advance.

Thanks for the info.
I was trying to use make an adjustable triangle shape using three free rectangles comped on top of each other(see picture):
"Square One" is locked to a diameter of one and doesn't move. It forms the top side of the triangle.
Squares Two and Three are located one unit below the first ones. Square two rotates from it's top left corner (via angle slider) to form the second side of the slider. It's length can be changed (.05-1) by a second slider.
Square Three is similar to Square 2 except it swings from the top left corner to form the third side of the triangle. I was fooling around with different versions of
c2 = a2 + b2 − 2ab cos©
via math nodes to get the correct angle and size for C, but can't quite get it to work. Is it possible? The most practical approach?

And the code in FF7

Triangles Meeting.ffxml

Thanks! That's very close to what I had in mind.
What I'm still trying to figure out is whether or not it's possible to
1. (Sliders) adjust the length and angle of the blue shape (specifically, at it's pivot point where it meets the green corner)
2. and have the red shape pivot/change size to complete the triangle.

Quote
Rachel Duim wrote: I went with the simple solution (just angle). Will take a look at adding the length… super busy when time allows.

No worries. Take your time.
In the meantime I have some ideas of how it to put it together, so if I get something that works I'll post it here.

The component is ArcSine. Here's a screenshot using rotation units. ArcSine(0.7122...) returns 0.1261... in rotations which is 45.4 degrees. And yes, do not round off any results.