Prove that $\cos20°\cos40°\cos60°\cos80°=\frac{1}{16}.$
12414
prove that : $\cos x \cdot \cos(x-60^{\circ}) \cdot \cos(x+60^{\circ})= \frac14 \cos3x$
148207
Express $\cos 6\theta $ in terms of $\cos \theta$
98745
To prove $(\sin\theta + \csc\theta)^2 + (\cos\theta +\sec\theta)^2 \ge 9$
40615
Solve for $x$ in the $80^\circ$-$80^\circ$-$20^\circ$ triangle
13297
Prove the following trigonometric identity without a calculator involved
135895
Proving the bounds of cosine
139065
Proving $\csc\frac\alpha2+\csc\frac\beta2+\csc\frac\gamma2 \ge 6$, where $\alpha$, $\beta$, $\gamma$ are the angles of a triangle
100895
Prove $1 + \cos 2C - \cos 2A - \cos 2B = 4\sin A\sin B\cos C$ for $A$, $B$, $C$ the angles of a triangle
72377
Show that $\sum_{n=1}^\infty r^n\cos(n\theta)=\dfrac{r\cos\theta -r^2}{1-2r\cos\theta+r^2}$ whenever $0<r<1$.
76490
Proving that $\cos(\arcsin(x))=\sqrt{1-x^2}$
102649
Prove that $\int_0^1\frac{x\ln (1+x)}{1+x^2}dx=\frac{\pi^2}{96}+\frac{\ln^2 2}{8}$
115128
How do I show this $\cos^2(\arctan(x))=\frac{1}{1+x^2}$
22058
Prove that $\cos(\pi/7)$ is root of equation $8x^3-4x^2-4x+1=0$
59003
Product of cosines: $ \prod_{r=1}^{7} \cos \left(\frac{r\pi}{15}\right) $
12646
In acute angle triangle, prove that $\cos (A-B) \cos (B-C) \cos (C-A)\ge 8\cos A \cos B \cos C$
145632
Proving $\frac{1}{\cos^2\alpha}<\frac{\tan\beta-\tan\alpha}{\beta-\alpha}<\frac{1}{\cos^2\beta}$
106355
How to prove Lagrange trigonometric identity