Sum of $\sum_{k=1}^n\sin{k\theta}$
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
72377
Show that $\sum_{n=1}^\infty r^n\cos(n\theta)=\dfrac{r\cos\theta -r^2}{1-2r\cos\theta+r^2}$ whenever $0<r<1$.
3798
Finding formula for sum $S_n = \sum_{i=1}^n i(i-1)$
134311
How to determine equation for $\sum_{k=1}^n k^3$
116360
Sum of n-th roots of unity
120976
Proving $\sum_{k=0}^{n}k{n\choose k}^2 = n{2n-1 \choose n-1} $
71413
Proving complex series $1 + \cos\theta + \cos2\theta +... + \cos n\theta $
108401
Sum of binomial coefficients $\sum_{k=0}^{n}(-1)^k\binom{n}{k}\binom{2n - 2k}{n - 1} = 0$
58247
Prove $\sum_{k=0}^n \binom{n+k}{k}=\binom{2n+1}{n}$
30518
Formula for $\sum_{k=1}^n \frac{1}{k(k+1)(k+2)}$?
128200
Sequence sum question: $\sum_{n=0}^{\infty}nk^n$
634
Closed form formula for $\sum\limits_{k=1}^n k^k$
101017
What is the sum of $\sum\limits_{i=1}^{n}ip^i$?
67271
$\sum_{n=-\infty}^{\infty}\frac{1}{(u +n)^2}=\frac{\pi^2}{(\sin \pi u)^2}$
14399
Calculate $\sum_{k=1}^n (-1)^{k+1} \binom{n}{k}\frac{1}{k}$
52987
$\sum_{n=-\infty}^{\infty}\frac{1}{(n+\alpha)^2}=\frac{\pi^2}{(\sin \pi \alpha)^2}$?
57549
Finding the sum $\sum_{k=1}^rk^2\binom {n-k}{r-k}$