F(x,n) = cos x + cos2x + cos3x + cos4x + ...+ cos(nx)2sin(x/2) F = 2sinx/2cosx + 2sinx/2cos2x + ...+ 2sinx/2 cos(nx) = sin(3x/2) - sin(x/2) + sin(5x/2) - sin(3x/2) + ...+ sin(n+1/2)x - sin(n-1/2)x= si...