Why is such sum of cosines always zero?
13297
Prove the following trigonometric identity without a calculator involved
101448
Is $\sin^2(z) + \cos^2(z)=1$ still true for $z \in \Bbb{C}$?
68968
Math.cos inaccurancy
156890
If $f$ and $g$ satisfy the sine/cosine addition formulae, then what is $g'(0)$?
48086
Why is this series of square root of twos equal $\pi$?
148343
The sum of the elements in a field of at least three elements is 0
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
34049
How can I understand and prove the "sum and difference formulas" in trigonometry?
97213
Why does $\sin(0)$ exist?
19962
Why is $\infty \cdot 0$ not clearly equal to $0$?
4340
Why does $1+2+3+\cdots = -\frac{1}{12}$?
46378
Trig substitution; why can we ignore the absolute value?
76941
How do you find the value of $\sum_{r=0}^{44} \tan^2(2r+1)$?
9960
Sum of an infinite series $(1 - \frac 12) + (\frac 12 - \frac 13) + \cdots$ - not geometric series?
143428
How to sum $\sum_{x=0}^{N-1} \cos{\left( \frac{2\pi x}{N} \right)}^{2}$?
117656
Division in Java always results in zero (0)?
39752
Is there a limit of $\cos(n!)$?