What is the trick on this problem ? I want to use that $1 + e^{ix} = 2 e^{i x/2} \cos(x/2) $ but it remains $r/n$ and I don't know what to do with this..
Thanks !
What is the trick on this problem ? I want to use that $1 + e^{ix} = 2 e^{i x/2} \cos(x/2) $ but it remains $r/n$ and I don't know what to do with this..
Thanks !
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