[R] Off topic --- help in locating a source.

Gabor Grothendieck
Wed, 17 May 2006 21:41:10 -0000

If a web site is suffiicent then:
http://functions.wolfram.com/ElementaryFunctions/Cos/23/02/


On 5/17/06, Rolf Turner <rolf at math.unb.ca>
wrote:
> Apologies for the off-topic question; as usual I'm trying to draw
> upon the unparalleled knowledge and sagacity of the r-help list.
> Please reply off-list if you can help me out.
>
> A collaborator of mine found a formula we need, on sheets which he had
> photocopied out of a book, some years ago.  He cannot remember which
> book (he's getting to be as senile and forgetful as I am, poor
> bloke!).  He thinks it was (and it appears to have been) a large
> encylopedic tome devoted to extensive tables of formulae, integrals
> and series, and stuff like that.
>
> The formula in question is
>
>         oo   1              1             1
>        SUM  --- cos(k*x) = --- ln (----------------)   0 < x < 2*pi
.
>        k=1   k              2       2*(1 - cos(x))
>
> (I.e. the right hand side is a function whose Fourier coefficients
> are 1/k, k > 0).
>
> Note that ``oo'' is my attempt to render the infinity symbol in
> ASCII.
>
> Does anyone know of a source where this formula may found/cited?
> (It doesn't *have* to be the same source from which my collaborator
> originally copied it!)  It must be well-known/in lots of books,
> mustn't it?   Said he, hopefully.
>
> Thanks for any assistance.
>
>                                cheers,
>
>                                        Rolf Turner
>                                        rolf at math.unb.ca
>
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