Prove $\cos \frac{\pi}5-\cos \frac{2 \pi}5=\frac12$ but without finding $\cos \frac{ \pi}5$
56934
How do we prove $\cos(\pi/5) - \cos(2\pi/5) = 0.5$ ?.
95786
Sum $\frac{1}{6} + \frac{5}{6\cdot 12} + \frac{5\cdot 8}{6\cdot 12\cdot 18} + \frac{5\cdot 8\cdot 11}{6\cdot 12\cdot 18\cdot 24}+\ldots$
70522
$y^2 = \frac{x^5 - 1}{x-1}$ & $x,y \in \mathbb{Z}$
24670
Find $x$: $5\cos(x) = 2\sec(x)-3$
134470
Prove $\frac{k^7}7+\frac{k^5}5+\frac{2k^3}3-\frac k{105}$ is a integer by mathematical induction
86454
How to prove $\cos\left(\pi\over7\right)-\cos\left({2\pi}\over7\right)+\cos\left({3\pi}\over7\right)=\cos\left({\pi}\over3 \right)$
35529
Prove that $\sin x+2x\ge\frac{3x(x+1)}{\pi}$ for all $x\in [0,\frac{\pi}{2}]$
47783
why $1+\frac{1}{1+\frac{1}{\frac{1}{1+\dots}}}$ cannot be equal to $\frac{1-\sqrt{5}}{2}$
12414
prove that : $\cos x \cdot \cos(x-60^{\circ}) \cdot \cos(x+60^{\circ})= \frac14 \cos3x$
50777
Prove that $4\sin\frac{2\pi}{7}- \tan\frac{\pi}{7}= \sqrt{7}$ .
24358
Finding $\int \frac{dx}{a+b \cos x}$ without Weierstrass substitution.
53307
how to strictly prove $\sin x<x$ for $0<x<\frac{\pi}{2}$
66872
Exact values of $\cos(2\pi/7)$ and $\sin(2\pi/7)$
10289
Need help in proving that $\frac{\sin\theta - \cos\theta + 1}{\sin\theta + \cos\theta - 1} = \frac 1{\sec\theta - \tan\theta}$
60462
Prove that $\frac{ 5^{125}-1}{ 5^{25}-1}$ is a composite number
41191
How to prove this $\pi$ formula?
65645
Express $w$ and $\frac1w$ for $w=\frac {\sqrt2+\sqrt3}{\sqrt5-\sqrt3}$ in the simplest form with a rational denominator