General observations about series, of which the terms arising for the sines or cosines of multiplied angles come forth
This paper, along with E592 and E636, seems to consider the binomial expansion of (1+z)n in the case where z is complex.
Original Source Citation
Nova Acta Academiae Scientiarum Imperialis Petropolitanae, Volume 7, pp. 87-98.
Opera Omnia Citation
Series 1, Volume 16A, pp.163-177.