Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.)

share|cite|improve this question
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
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… for more details. – user17762 Oct 29 '12 at 2:14

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?

share|cite|improve this answer

Hint: Apply $$\sin(A+B)=\sin A \cos B+\cos A \sin B$$ $$\cos(A+B)=\cos A \cos B- \sin A \sin B$$

share|cite|improve this answer
Even if it was meant to be a hint, you should give some more detail. For example, the OP has to use the negative version of this rule, and the OP has to know that $\cot(x)=\frac{\cos(x)}{\sin(x)}$. Otherwise the answer won't make that much sense. Further, please use LaTeX next time to format your formulas, there is a guide on meta. – wythagoras Aug 16 '15 at 5:49

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.