Proof of "clear" infinite trigonometric equality.
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
132411
Fourier series coefficients proof
14386
Proof of an equality involving cosine $\sqrt{2 + \sqrt{2 + \cdots + \sqrt{2 + \sqrt{2}}}}\ =\ 2\cos (\pi/2^{n+1})$
13747
Proof of $\int_0^\infty \frac{\sin x}{\sqrt{x}}dx=\sqrt{\frac{\pi}{2}}$
13297
Prove the following trigonometric identity without a calculator involved
53307
how to strictly prove $\sin x<x$ for $0<x<\frac{\pi}{2}$
123476
Prove $[\sin x]' = \cos x$ without using $\lim\limits_{x\to 0}\frac{\sin x}{x} = 1$
27513
Trigonometric bounds
79117
Proof that the harmonic series diverges (without improper integrals)
16253
Proof that $|\sin(nx)| \le n|\sin(x)|$
54512
How do I prove: $\cos (\theta + 90^\circ) \equiv - \sin \theta $
63679
Picture/intuitive proof of $\cos(3 \theta) = 4 \cos^3(\theta)-3\cos(\theta)$?
78120
Proof of Bernoulli's inequality
144713
Simple Calculus Proof
90475
Coordinate-free proof of $\operatorname{Tr}(AB)=\operatorname{Tr}(BA)$?
18967
Linear independence of $\sin(x)$ and $\cos(x)$
60761
Proof: $\cos^p (\theta) \le \cos(p\theta)$