Posted by **Riley** on Sunday, November 14, 2010 at 10:00pm.

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

- Pre-Calculus -
**Reiny**, Sunday, November 14, 2010 at 10:30pm
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 -
**Riley**, Sunday, November 14, 2010 at 10:41pm
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 -
**Reiny**, Sunday, November 14, 2010 at 10:54pm
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 -
**Daniel**, Sunday, November 14, 2010 at 11:00pm
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 -
**Reiny**, Sunday, November 14, 2010 at 11:18pm
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)

## Answer this Question

## Related Questions

- Pre Calc. - Use the sum or difference identity to find the exact value of sin255...
- Algebra 2/ trig - sin theta= 7/25, 0< theta < pi/2 cos beta=8/17, 0, beta...
- Math - Does 'using the unit circle' just mean that I use these: In Quadrant I, ...
- Calculus - I wanted to confirm that I solved these problems correctly (we had to...
- pre calc - suppose beta is an angle in the second quadrant and tan beta=-2. ...
- math - How would you establish this identity: (1+sec(beta))/(sec(beta))=(sin^2(...
- trig - If sin theta is equal to 5/13 and theta is an angle in quadrant II find ...
- easy trig - If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the ...
- simple trig - If sin(theta)=[sqrt(70)]/7 and theta is in Quadrant two, find the ...
- math (trig) - if cos 2 theta = -(1/3) and theta is in Quadrant 2, find sin theta...