It has been like a year since I took pre-calculus. Now were in the review section and were reviewing trig and I am struggling remembering much about the rules. In any case here is my problem:

Find cos(theta) and tan(theta) if sin(theta)=5/13 and (now here is the part throwing me off) 0 <= theta <= pie/2

I found that cos(theta)=194/13 and tan(theta)=5/194 I typed these answers in, and they were wrong. I am not sure why but I am almost positive it has something to do with the stipulation <= theta <= pie/2. Could someone please (not only show me the answers) but also explain how to deal with these types of stipulations?