(5)左边序列 x(n) m(m)=/(m n< n n>n X(z)=∑ r(nz ∑x(n)z+∑x(m)z n=1   = − =− − =− − = + = 2 2 1 0 ( ) ( ) ( ) ( ) n n n n n n n n x n z x n z X z x n z (5)左边序列      = 2 2 0, ( ), ( ) n n x n n n x n x(n) 0 n n 2 