Proving trigonometric equation $\cos(36^\circ) - \cos(72^\circ) = 1/2$
56934
How do we prove $\cos(\pi/5) - \cos(2\pi/5) = 0.5$ ?.
123476
Prove $[\sin x]' = \cos x$ without using $\lim\limits_{x\to 0}\frac{\sin x}{x} = 1$
138575
Proof that $\cos^2(x)\cosh^2(y) + \sin^2(x)\sinh^2(y) = -1 + \sin^2(x) - \sinh^2(y)$
58932
Hard contest type trigonometry proof
48824
Prove: $ \frac{1}{\sin 2x} + \frac{1}{\sin 4x } + \cdots + \frac{1 }{\sin 2^n x} = \cot x - \cot 2^n x $
156610
To prove the limit of $\frac{x^2+2\cos x-2}{x\sin^3 x}$ at zero is $1/12$
60230
Prove that $\frac{1+\sin\theta+i\cos\theta}{1+\sin\theta-i\cos\theta}=\sin\theta+i\cos\theta$
98745
To prove $(\sin\theta + \csc\theta)^2 + (\cos\theta +\sec\theta)^2 \ge 9$
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
122169
Prove $\sin(\pi/2)=1$ using Taylor series
32705
Trigonometric Equation : $\sin 96^\circ \sin 12^\circ \sin x = \sin 18^\circ \sin 42^\circ \sin (12^\circ -x)$
29604
How to solve $\sin x +\cos x = 1$?
110261
Value of $ \cos 52^{\circ} + \cos 68^{\circ} + \cos 172^{\circ} $?
45227
If $\sin \theta+\cos\theta+\tan\theta+\cot\theta+\sec\theta+\csc\theta=7$, then $\sin 2\theta$ is a root of $x^2 -44x +36=0$ My own bonafide attempt.
155148
Why is $\sin 30^\circ=\frac{1}{2}$
141787
Anybody know a proof of $\prod_{n=1}^\infty\cos(x/2^n)=\sin x/x$.
13297
Prove the following trigonometric identity without a calculator involved