What is the period of $\cos(x)=1-\frac{x^2}{2!}+\frac{x^4}{4!}-\frac{x^6}{6!}\cdots$?
6465
How to prove periodicity of $\sin(x)$ or $\cos(x)$ starting from the Taylor series expansion?
135488
How to find period of the interpolating function
75721
No. of real solutions of the equation $2 \cos (\frac{x^2 + x}{6}) = 2^x + 2^{-x} $
4644
Finding the limit $\lim \limits_{n \to \infty}\ (\cos \frac x 2 \cdot\cos \frac x 4\cdot \cos \frac x 8\cdots \cos \frac x {2^n}) $
82586
Why is cos -x equal to cos x?
32792
Proving: $\cos A \cdot \cos 2A \cdot \cos 2^{2}A \cdot \cos 2^{3}A ... \cos 2^{n-1}A = \frac { \sin 2^n A}{ 2^n \sin A } $
21780
Period of the sum/product of two functions
56059
If $\frac{\sin^4 x}{a}+\frac{\cos^4 x}{b}=\frac{1}{a+b}$, then show that $\frac{\sin^6 x}{a^2}+\frac{\cos^6 x}{b^2}=\frac{1}{(a+b)^2}$
84420
When is $\sin(x) = \cos(x)$?
58633
Proof of the formula $1+x+x^2+x^3+ \cdots +x^n =\frac{x^{n+1}-1}{x-1}$
5747
$\cos(\arcsin(x)) = \sqrt{1 - x^2}$. How?
79684
Finding $\lim \limits_{x \to 0} \frac{1 - \cos x}{x}$, given $\lim \limits_{x \to 0} \frac{\sin x}{x} = 1$
35754
Is $f(x)=\sin(x^2)$ periodic?
13864
$\prod_{k=0}^{\infty} \cos(x \cdot 2^{-k}).$
30429
How to prove $\cos \frac{2\pi }{5}=\frac{-1+\sqrt{5}}{4}$?
62576
How to find $\lim_{n\to\infty}\frac{1!+2!+\cdots+n!}{n!}$?
111102
Prove the Trigonometric Identity: $\frac{\sin x}{1-\cos x} = \frac{1+\cos x}{\sin x}$