Plotting an Exponential Fourier Series

[polaris90]

I'm having some problem in determining the phase of an exponential Fourier series. I know how to determine the coefficient which in turn gives me the series after I multiply by $e^-(jωt)$
I can determine the amplitude by dividing the coefficient by 2 $|Dn| = Cn/2$
Now my question is how to determine the phase angle. My book only gives me $ø=∠Dn$ and it doesn't explain how they get the values. Do I have to expand Cn into its real and imaginary parts and then calculate the angle using tan^-1(-bn/an) as I would when using sines and cosines?

 

[Baluncore]

Do I have to expand Cn into its real and imaginary parts and then calculate the angle using tan-1(-bn/an) as I would when using sines and cosines?

Yes.