Determinations of Analogues of Gauss Sums and Other Trigonometric Sums
  Explicit determinations of several classes of trigonometric sums are given. These sums can be viewed as analogues or generalizations of Gauss sums. In a previous paper, two of the present authors considered primarily sine sums associated with primitive odd characters. In this paper, we establish two general theorems involving both sines and cosines, with more attention given to cosine sums in the several examples that we provide. 
Matthias Beck, Bruce C. Berndt, O-Yeat Chan, and Alexandru Zaharescu