I'm trying to solve this exercise:

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And the solutions manual states that the resolution is this one:

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but I can not understand the last step, which is indicated with an arrow. Also, how do you find the ROC.


Multiply the numererator and denominator by $z^N$ and factor out (in the denominator) $z^{N-1}$.

  • $\begingroup$ dunno why this answer was downvoted, but i balanced it out with an upvote. $\endgroup$ Mar 14 '19 at 23:36
  • $\begingroup$ probably because I didn’t use math style font. thanks for edit. $\endgroup$
    – zoulzubazz
    Mar 15 '19 at 10:53

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