How do I proceed in proving that $\cos 20^o\cos 40^o\cos 60^o\cos 80^o = \frac{1}{16}$
12414
prove that : $\cos x \cdot \cos(x-60^{\circ}) \cdot \cos(x+60^{\circ})= \frac14 \cos3x$
99012
Finding an angle in a $80^\circ$-$80^\circ$-$20^\circ$ triangle (variant involving $70^\circ$ and $60^\circ$)
35948
How to prove $D^n/S^{n-1}\cong S^n$?
48503
Proving : $ \bigl(1+\frac{1}{n+1}\bigr)^{n+1} \gt (1+\frac{1}{n})^{n} $
148094
Show that $e^3 > 20$
120795
Showing that $\sin^2x\cdot\sin^22x\cdot\sin^24x\cdot\sin^28x\cdots\sin^22^nx\leq\frac{3^n}{4^n}$
23727
How can I deduce $\cos\pi z=\prod_{n=0}^{\infty}(1-4z^2/(2n+1)^2)$?
14386
Proof of an equality involving cosine $\sqrt{2 + \sqrt{2 + \cdots + \sqrt{2 + \sqrt{2}}}}\ =\ 2\cos (\pi/2^{n+1})$
2251
Can someone give me a hint on how to prove this?
57041
How would you prove that $2^{50} < 3^{33}$ without directly calculating the values
152039
Prove that $a^{2^n}=1 \mod 2^{n+2}$
30429
How to prove $\cos \frac{2\pi }{5}=\frac{-1+\sqrt{5}}{4}$?
27579
Evaluating the infinite product $ \prod\limits_{n=1}^{\infty} \cos(\frac{y}{2^n}) $
138683
Proving $\prod_{i=2}^{i=n} \left(1-\frac{1}{i^2}\right) = \frac{n+1}{2n}$ by induction
20964
Proof that $n^2 < 2^n$
142673
Evaluate $\tan^{2}(20^{\circ}) + \tan^{2}(40^{\circ}) + \tan^{2}(80^{\circ})$
100320
Prove that $\cos\frac {2\pi}{7}+ \cos\frac {4\pi}{7}+ \cos\frac {8\pi}{7}=-\frac{1}{2}$