证:X(z)= x(n)2 dx(z) d v x(n) n dz dz 1=-00 dz x(n-nz nx(n) z 1=-0 1=-00 ur(n dX(=) ZTInx(n)I R<|<R( ) ( ) n n X z x n z 证: ( ) ( ) ( ) ( ) n n n n dX z d d x n z x n z dz dz dz 1 1 ( )( ) ( ) n n n n x n n z z nx n z 1 z ZT[nx(n)] ( ) [ ( )] x x dX z ZT nx n z R z R dz