# z-transform help

I'm trying to solve this exercise:

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

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) $$z^{N-1}$$.

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