()=∑cke"N k=<N 系数的确定 (n)e k=<N j(k-m)n C (交换求和顺序) k=<N> Ln=<N> 在上式右边对n求和时,只当k=m时为非零,所以有: Jm-arn NIne N k=1∑x()% n=<N: = = k N j k n N k N x n c e 2 ( ) 系数的确定 ( ) ( ) 2 2 2 2 ( ) 交换求和顺序 = = = − = = = − = − n N j k m n k N k n N k N j k n k j m n n N j m n N N N N N c e x n e e c e 在上式右边对 n 求和时,只当 k = m 时为非零,所以有: x n e c m N n N jm n N N = = − 2 ( ) = − = n N j k n k N N x n e N c 2 ( ) 1