Searching for formulas? Is there a site to search for formulas? I often come up with formulas that I would like to know the name, where they are used or what they are related to. One would type, for example, $\sin(a)\cos(b)+\sin(b)\cos(a)$ and it would intelligently associate it with the sum of sines formula. I know this would be no trivial service but I find it would be a great tool.
 A: What about this?
http://www.wolframalpha.com/
A: Unfortunately the existing search engines do not have that capability yet. You may check back in a year, there will be. (Trust me!)
In the meanwhile, maybe this one can be of some help
A: I think more specifically Dokkat is looking for http://www.jackpo.org/files/formulas.pdf (something of this sort)
A: Wolfram|Alpha is the kind of thing you're looking for. For now, unfortunately, there aren't so many engines which allows you to search for knowledge rather than just results. For the sake of posting an answer though, I have heard about The Springer LaTeX search http://www.latexsearch.com/ but I'm not sure how useful could it be.
Morals of the story, you can always use a combination of Google, W|A, math.SE search bar, and question posting.
A: The search engine at formulasheet.com lets you search for formulas by typing in keywords (it also provides search suggestions). It searches Wikipedia's vast array of formulas as well as user-shared formulas and a small but growing formula database of their own. It does not however provide a means to search based on the source such as sin(a)cos(b)+sin(b)cos(a) as you requested, but it does do the reverse, for example http://formulasheet.com/#q|ev|Sine%20sum%20and%20difference%20identity.
