Question

How do I decide when to use sin, cos, or tan? I know the ratios for each one and I can recognize the parts of a triangle, I just don't know how you decide which one to use in a problem.

Answer 1

Well you're generally given an angle, and a side length,
and asked to find another side length, right? :)

Answer 2

Example drawn above.

Answer 3

Let's label these three sides `in relation to where the angle is positioned`.