Explanation of this hint involving the summation of cosine and sine
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
111102
Prove the Trigonometric Identity: $\frac{\sin x}{1-\cos x} = \frac{1+\cos x}{\sin x}$
103347
combinatorial proof of summation
150928
Summation of a trigonometric series - $\frac{\sin n}{n}$
140984
Sum of Cosine/Exponential
91521
Ambiguity of notation: $\sin(x)^2$
42424
Riemann sum of $\sin(x)$
67271
$\sum_{n=-\infty}^{\infty}\frac{1}{(u +n)^2}=\frac{\pi^2}{(\sin \pi u)^2}$
6345
Is the $\sum\sin(n)/n$ convergent or divergent?
59014
Prove that $\sin(2A)+\sin(2B)+\sin(2C)=4\sin(A)\sin(B)\sin(C)$ when $A,B,C$ are angles of a triangle
46353
Proof that $\cos(\pi/3)=1/2$
104427
Sines and cosines of angles in arithmetic progression
27628
Solving $a \sin\theta + b \cos\theta = c$
13297
Prove the following trigonometric identity without a calculator involved
82391
Why does $\sum_{k=1}^{\infty}\frac{{\sin(k)}}{k}={\frac{\pi-1}{2}}$?
24656
Proving that $\frac{\csc\theta}{\cot\theta}-\frac{\cot\theta}{\csc\theta}=\tan\theta\sin\theta$
149850
Methods for determining the convergence of $\sum\frac{\cos n}{n}$ or $\sum\frac{\sin n}{n}$