Is this notation mathematically-correct? $\cot\alpha\pm\tan\alpha=\frac2{{\sin\atop\tan}(2\alpha)}$ I have a question.
Look at the following expression:

$$\cot\alpha\pm\tan\alpha=\frac2{{\sin\atop\tan}(2\alpha)}$$

Is it written well, according to the laws of mathematical language?
In that formula, I meant that in case of '$+$' we will use the $\sin()$ function, and in case of '$-$' we will use the $\cos()$ function.
If it's not good, is there a good way (a mathematically-correct way) of writing both cases (both '$+$' and '$-$') in one formula?
by the way,
do you think that this general explanatory is good and understandable?

$a \pm b = {func1\atop func2}(c)$

means:

$a+b=func1(c)$
$a-b=func2(c)$

Thank you,
Tom
 A: You ask:

"Is it written well, according to the laws of mathematical language?"

There aren't really laws, just guidelines. Mathematics isn't a programming language. So I agree with J.M.'s comment 100%.
But, to make the meaning of the notation a little, clearer, you might want to write something more along the lines of
$$\cot\alpha\left\{\begin{matrix}+\\-\end{matrix}\right\}\tan\alpha=\frac{2}{\left\{\begin{matrix}\sin\\\tan\end{matrix}\right\}(2\alpha)}$$
or something like that. Either way, make sure to explain in text what you mean.
A: It's not standard notation.  I would not count on a reader correctly understanding it, unless you explain it.
You could introduce it as your own special notation, but unless you feel it makes a huge difference in the clarity or conciseness of your work, I would not do so.  Readers tend to get annoyed by gratuitous use of non-standard notation.  Don't use it just to save writing one or two lines.  But if there are dozens of places in your paper where it saves duplication, then it might be worth considering.
