How to prove Lagrange trigonometric identity
65698
Proving $\sum\limits_{k=0}^{n}\cos(kx)=\frac{1}{2}+\frac{\sin(\frac{2n+1}{2}x)}{2\sin(x/2)}$
76490
Proving that $\cos(\arcsin(x))=\sqrt{1-x^2}$
48394
Proving bessel identity $[J_0(x)]^2 + 2[J_1(x)]^2 + 2[J_2(x)]^2 + \cdots = 1$ and $|J_0(x)|\le 1$
60559
How prove this $x^3<\sin^2{x}\tan{x},x\in\left(0,\dfrac{\pi}{2}\right)$
113080
Prove $\tan\big(\frac{\pi}{2} -\theta \big) = \cot \theta$
122490
Proof of Parseval's identity
126701
How to prove that $d \sin(x)/dx = \cos(x)$ without circular logic such as L'Hôpital's rule?
71413
Proving complex series $1 + \cos\theta + \cos2\theta +... + \cos n\theta $
12414
prove that : $\cos x \cdot \cos(x-60^{\circ}) \cdot \cos(x+60^{\circ})= \frac14 \cos3x$
58526
Proving Legendre's Formula
98745
To prove $(\sin\theta + \csc\theta)^2 + (\cos\theta +\sec\theta)^2 \ge 9$
42384
Сanonical form of a quadratic form by Lagrange's method
11711
Prove trigonometry identity for $\cos A+\cos B+\cos C$
52311
Prove that $0 \le \frac{1+\cos\theta}{2+\sin\theta} \le \frac{4}{3}$ for all real $\theta$.
7712
How to prove the both identity (matrix)
120148
prove this properties of triangles trigonometric question
54512
How do I prove: $\cos (\theta + 90^\circ) \equiv - \sin \theta $