How to prove that $\cos(\pi÷11)+\cos(3\pi÷11)+\cos(5\pi÷11)+\cos(7\pi÷11)+\cos(9\pi÷11)=0.5$?
132065
Prove sum of $\cos(\pi/11)+\cos(3\pi/11)+...+\cos(9\pi/11)=1/2$ using Euler's formula
38975
Find the value of $\textrm{cosec}^2\left(\frac\pi7\right) +\textrm{cosec}^2\left(\frac{2\pi}7\right)+\textrm{cosec}^2\left(\frac{4\pi}7\right)$
71413
Proving complex series $1 + \cos\theta + \cos2\theta +... + \cos n\theta $
26608
How to show that $\int_{0}^{\pi}{\sin^5 x\over 1+\cos^3 x}\mathrm dx=\ln 3?$
17168
Find the value of $\sin\frac{2\pi}{7}+\sin\frac{4\pi}{7}+\sin\frac{8\pi}{7}$
104321
Prove that $1 + \cos\alpha + \cos\beta + \cos\gamma = 0$
104384
Trigonometric identity: $\frac {\tan\theta}{1-\cot\theta}+\frac {\cot\theta}{1-\tan\theta} =1+\sec\theta\cdot\csc\theta$
35244
Prove $\sin^2\theta + \cos^2\theta = 1$
74143
Simplifying and evaluating $\cot 70^\circ+4\cos 70^\circ$
100320
Prove that $\cos\frac {2\pi}{7}+ \cos\frac {4\pi}{7}+ \cos\frac {8\pi}{7}=-\frac{1}{2}$
60761
Proof: $\cos^p (\theta) \le \cos(p\theta)$
11711
Prove trigonometry identity for $\cos A+\cos B+\cos C$
141645
Trigonometric series sum proof
17188
Simplify $\cos(n \pi)$ and $\sin(n \pi)$ when n is an integer
54512
How do I prove: $\cos (\theta + 90^\circ) \equiv - \sin \theta $
66872
Exact values of $\cos(2\pi/7)$ and $\sin(2\pi/7)$
76490
Proving that $\cos(\arcsin(x))=\sqrt{1-x^2}$