Question 76
Find all real $x$ in $[0, 2\pi)$ for which all terms of the sequence
$$
a_n = \frac{1}{\cos(nx)}
$$
are integers.
$$
a_n = \frac{1}{\cos(nx)}
$$
are integers.
MathNet 2010 — Part 06 Question 76
Math Olympiad Vault · MathNet 2010 — Part 06