。有周期序列的傅里叶级数： xn]=∑a4e2rn &=卡∑ k=<N> n=<N> ÷因为在-N<=n<=N,区间的一个周期上x[n]=x[n] 1 ak= x[n]ek(2π/w)n N n=-N1 =人艺nk2aw N n=-∞ 有周期序列的傅里叶级数：  因为在 -N1 <= n<=N2区间的一个周期上   (2 / ) (2 / ) [ ] 1 [ ] jk N n k k N jk Nn k n N xn ae a xne N π π =< > − =< > = =    xn xn [] [] = 2 1 (2 / ) (2 / ) 1 [ ] 1 [ ] N jk Nn k n N jk Nn n a xne N xne N π π − =− +∞ − =−∞ = =  