Hi,
iS THERE Any one out there who can provide an expression for the sum of n terms:
i*X* COS i*X
where X is in radians, and i varies from 1 to n?
Thanks in advance for your help.
Cheers
How about this use the following lemma
$\displaystyle \sum_{n=1}^{m}n\cdot x^n=\frac{x^{m+1}(mx-m-1)+x}{(x-1)^2}$
So your sum of $\displaystyle \sum_{n=1}^{m}xn\cos(nx)=x\Re\left\{\sum_{n=1}^{m} ne^{inx}\right\}$ and apply the above lemma with $\displaystyle x=e^{ix}$