Why are $sin(x)$ and $cos(x)$ irrational for (non-zero) rational values of $x$?
125812
Is sin(x) necessarily irrational where x is rational?
103376
Is $\sin(p \pi/q)$ necessarily an algebraic number?
97213
Why does $\sin(0)$ exist?
111094
Help with proving that $\pi$ is irrational
80304
Roots of $\,ax^2+bx+c\,$ are irrational if $a,b,c$ are odd integers
48225
Proving that $\sin1 $(radian) is irrational without using Taylor Series Expansion.
135967
What is the odd Fourier extension of $\sin x \cos(2x)$?
82321
Is $\cos(x) \geq 1 - \frac{x^2}{2}$ for all $x$ in $R$?
39461
What is the solution of $\cos(x)=x$?
123490
L'Hopital's rule and $\frac{\sin x}x$
53945
The square root of a prime number is irrational
87410
Are there real numbers that are neither rational nor irrational?
141273
When is $\sin(x)$ rational?
126701
How to prove that $d \sin(x)/dx = \cos(x)$ without circular logic such as L'Hôpital's rule?
40556
Why is $\sin(\alpha+\beta)=\sin\alpha\cos\beta+\sin\beta\cos\alpha$
84420
When is $\sin(x) = \cos(x)$?
106828
If $0 \lt x \lt \frac{\pi}{2}$, is $\cos(x) \le \frac{\sin(x)}{x} \le \frac{1}{\cos(x)}$?