PreCalculus
posted by Riley .
If sin(theta)=15/17 and cos(beta)=(5/13 (both theta and beta are in quadrant II) find tan(theta+beta)

You should recognize the 8,15,17 and 5,12,13 rightangled triangles
so in II if
sinØ= 15/17, then cosØ = 8/17 and tanØ =  15/8
cosß = 5/13 , then sinß = 12/13 and tanß = 12/5
tan(Ø+ß) = (tanØ + tanß)/(1  tanØtanß)
= ....
you finish the arithmetic. 
Ok i understand until you say that tan(theta) +tan(beta) needs to be divided by 1tan(theta)tan(beta) where does that come from?

I assumed you knew the formulas, since you have know them to do these kind of problems
look under "other identities"
http://library.thinkquest.org/20991/alg2/trigi.html 
I do but why did u use that one. Im trying to understand because i have a test tomorrow and i have to do well on it.

well, it asked for tan(Ø+ß) didn't it?
The letters themselves of course don't matter
e.g.
tan(A+B) =(tanA + tanB)/(1 tanAtanB)