# Pre-Calculus

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If sin(theta)=15/17 and cos(beta)=(-5/13 (both theta and beta are in quadrant II) find tan(theta+beta)

• Pre-Calculus -

You should recognize the 8,15,17 and 5,12,13 right-angled 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.

• Pre-Calculus -

Ok i understand until you say that tan(theta) +tan(beta) needs to be divided by 1-tan(theta)tan(beta) where does that come from?

• Pre-Calculus -

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

• Pre-Calculus -

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.

• Pre-Calculus -

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)

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