How to prove infinite product converging to sin and cos?
24311
Proving $\frac{\sin x}{x} =\left(1-\frac{x^2}{\pi^2}\right)\left(1-\frac{x^2}{2^2\pi^2}\right) \left(1-\frac{x^2}{3^2\pi^2}\right)\cdots$
53213
How to prove that $\lim(\underset{k\rightarrow\infty}{\lim}(\cos(|n!\pi x|)^{2k}))=\chi_\mathbb{Q}$
141645
Trigonometric series sum proof
158357
Infinite Product $\prod_{n=1}^\infty\left(1+\frac1{\pi^2n^2}\right)$
119232
Convergence/Divergence of infinite product
122990
How can I prove that $\lim\limits_{n\to\infty}\frac{n+\sin n}{n+1} = 1$
155777
Show that infinite Cartesian product is uncountable
135895
Proving the bounds of cosine
127380
Use vectors to prove $\cos(\beta - \alpha) = \cos \alpha \cos\beta + \sin\alpha \sin\beta$
13864
$\prod_{k=0}^{\infty} \cos(x \cdot 2^{-k}).$
35244
Prove $\sin^2\theta + \cos^2\theta = 1$
55869
Use the Maclaurin series to prove that $e^{i\theta} = cos(\theta) + isin(\theta)$
143857
How to prove absolute summability of sinc function?
14730
How prove this $\lim_{n\to \infty}\sin{n^m}$ divergent.
125887
Evaluate an infinite product in a closed form $\prod\limits_{n=1}^{\infty} \frac{1}{1+\pi^{1/{2^n}}}$
68320
Infinite Product $\prod\limits_{k=1}^\infty\left({1-\frac{x^2}{k^2\pi^2}}\right)$
35855
Closed form for an infinite product