w*******d
发帖数: 3 | 1 1) to tell if x(n) is real or not, you could compare X(z) with X*(z*) (=Z[x*
(n)]. Since [cosh(aZ*)]*=cosh(az), it should be real.
2) For a system (or signal) to be causal, its ROC should include infinity.
Otherwise it is noncausal. For a system to be anticausal, its ROC should
include zero. Since cosh(aZ) is infinite for Z=infinity, so it could not be
causal. cos(aZ)=1 when Z=0, so zero is included in the ROC. Therefore, cosh(
aZ) is anticausal. |
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