Solving Right Triangle question

[Gooby]

Homework Statement

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.

Homework Equations

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.

 

[grzz]

In a right-angled traingle there is always the HYPOTHENUSE i.e. the greatest side. Then if the angle 40deg (in the given diagram) is taken, the side of size 2 will be the adjacent side with respect to 40 deg but this SAME side will then be the opposite side with respect to the other angle 50 deg.

So one can use cos40 = adj/hyp = 2/hyp or one can use sin50 = opp/hyp = 2/hpy.

Infact one can check with the calculator that cos40 = sin50.