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Find the exact value of $$\cot(v-u)$$ given that $\sin u=−3/5$ and $\cos v = − 7/25$ (Both $u$ and $v$ are in Quadrant III.)

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Please don't just dump problems here --- tell us why you are interested in the question, what you know about it, where you get stuck in solving it, and so on. –  Gerry Myerson Oct 29 '12 at 2:13
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Dear MOG, Welcome to math.SE. since you are a new user, we wanted to let you know a few things about the site. In order to get the best possible answers, it is helpful if you say what your thoughts on the problem are so far; this will prevent people from telling you things you already know, and help them write their answers at an appropriate level. Further, it would be better if you could typeset your problem so that it is easy for people to read. Kindly look meta.math.stackexchange.com/questions/107/… for more details. –  user17762 Oct 29 '12 at 2:14
    
Exact value of which trig function? –  André Nicolas Oct 29 '12 at 2:15
    
trig function of cot( v-u) –  MOG Oct 29 '12 at 2:19
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1 Answer

Some hints:

Do you know a formula relating the cotangent to the sine and cosine?

Do you know formulas relating $\sin(A+B)$ and $\cos(A+B)$ to $\sin A,\sin B,\cos A, \cos B$?

Do you know a formula relating $\sin C$ and $\cos C$?

Do you know which trig functions are positive in which quadrants?

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