(3)x(n)=( 0< N 解:X(A)=∑x(nWR() nk ∑x(n)e"R、(k) 丌 ∑6(m R(k R(k)1 2 0 ( ) ( ) N j nk N N n x n e R k 1 2 0 0 ( ) ( ) N j nk N N n n n e R k 0 2 ( ) j n k N N e R k (3) 0 x(n) (n n ) 0 0 n N 1 0 ( ) ( ) ( ) N nk N N n X k x n W R k 解: