Sign of a trigonometric sum
103419
Inequality $\sum\limits_{1\le k\le n}\frac{\sin kx}{k}\ge 0$ (Fejer-Jackson)
80177
Sum from $n=1$ to $N$ of $\sin(nx)/2^n$
4573
Explicitly finding the sum of $\arctan(1/(n^2+n+1))$
87934
Deducing $\sin x + \cos x \ge 1$ from $(\sin x + \cos x)^2 = 1 + 2 \sin x \cos x$
83359
Complex number identity by trigonometry
49262
Evaluation of Sum of $ \sum_{n=1}^{\infty}\frac{\sin (n)}{n}$.
21855
Prove $\sum_{n=1}^{\infty}\arctan{\left(\frac{1}{n^2+1}\right)}=\arctan{\left(\tan\left(\pi\sqrt{\frac{\sqrt{2}-1}{2}}\right)\cdots\right)}$
17769
Show that $\frac{\sin x}{\cos 3x}+\frac{\sin 3x}{\cos 9x}+\frac{\sin 9x}{\cos 27x} = \frac{1}{2}\left(\tan 27x-\tan x\right)$
148069
Different Sum signs
18399
Prove this inequality $\sum \cos{A}\ge\frac{1}{4}(3+\sum\cos{(A-B)})$
17188
Simplify $\cos(n \pi)$ and $\sin(n \pi)$ when n is an integer
150928
Summation of a trigonometric series - $\frac{\sin n}{n}$
96367
Intuition of Addition Formula for Sine and Cosine
84420
When is $\sin(x) = \cos(x)$?
54175
Prove the trigonometric identity $\sin^4{x} = \frac{3-4\cos{2x}+\cos{4x}}{8}$
81102
Cosine of the sum of two solutions of trigonometric equation $a\cos \theta + b\sin \theta = c$
82391
Why does $\sum_{k=1}^{\infty}\frac{{\sin(k)}}{k}={\frac{\pi-1}{2}}$?