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$$ a_q=2*real(f_q)/N,\hspace{1cm} b_q=-2*image(f_q)/N,\hspace{1cm}
q=1,2,...N/2-1 $$ $$ a_0=f_0/N \hspace{1cm}
a_{N/2}=f_{q=N/2}/N,\hspace{1cm} b_{N/2}=0 \hspace{1cm}(5) $$

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