Problem A. 697. (April 2017)
A. 697. For all primes \(\displaystyle p\ge3\), let
\(\displaystyle S(p) = \sum_{k=1}^{\frac{p-1}2} \tan \frac{k^2\pi}{p}. \)
\(\displaystyle (a)\) Show that \(\displaystyle p\equiv1\pmod4\) implies \(\displaystyle S(p)=0\).
\(\displaystyle (b)\) Show that if \(\displaystyle p\equiv3\pmod4\), then \(\displaystyle \dfrac{S(p)}{\sqrt{p}}\) is an odd integer.
(5 pont)
Deadline expired on May 10, 2017.
Statistics:
13 students sent a solution. 5 points: Bukva Balázs, Matolcsi Dávid, Schrettner Jakab, Williams Kada. 4 points: Imolay András, Kővári Péter Viktor. 2 points: 7 students.
Problems in Mathematics of KöMaL, April 2017