Inequalities for finite trigonometric sums. An interplay: with some   series related to Harmonic numbers
  An interplay between the sum of certain series related to Harmonic numbers and certain finite trigonometric sums is investigated. This allows us to express the sum of these series in terms of the considered trigonometric sums, and permits us to find sharp inequalities bounding these trigonometric sums. In particular, this answers positively an open problem of H. Chen (2010). 
Omran Kouba
math.CA