I am having trouble with right triangles. I understand how to use the formulas, however I don't know which angle is appropriate when using the formulas. For example, in this picture: http://imgur.com/C2lxg .
There was a problem in my book that had a triangle like this. The angles would change, ex. the 40 would become a 60, but you would always use the angle in that location to solve the triangle. I don't see why the angle in the 50 degree position was never used. I'm sure I am not making much sense, but hopefully someone can decipher this.
The Attempt at a Solution
I don't really have any work to show, because it's a theory question. Before, I thought you just always plugged in the first angle given, but on problems where the angles are switched, I don't know.