Can you explain how they go from the first line to the second? More specifically, what are the steps for making the negative exponential terms positive?
i.e. how does the third term: $-e^{j(4\pi t + \pi/3)}$ become $e^{-j(2\pi /3)} e^{j4\pi t}$ ?
This step shown above is part of a bigger question on finding Fourier Series.