Translations:Causality and stability of digital systems/13/es

${\begin{aligned}h_{k}=-a^{k}\mathrm {\;\;\;for\;\;\;} k=-{\rm {l,}}-{2,\ldots }\\h_{k}=0\mathrm {\;\;for\;\;\;} k=0,1,2,\ldots .\end{aligned}}$

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