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I have this question : enter image description here

I should now calculate power of y[n], where the formula enter image description here

well in the power's formula N which constant goes to infinity how could this be ? i see in the question that N=7 which is constant,then should N or KN go to infinity ?

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  • $\begingroup$ First, $y[n]$ can be written as a set just like $x[n]$. so between some range of $n$, it has a value, where it is 0 for all other. Secondly, this power formula looks correct, however I think that it shouldnt sum $x[n]$ but $y[n]$ (at you compute the power of $y[n]$). This together, can explain your struggle with $N$. as $y[n]$ is only nonzero for some range (and not upto infinity) $\endgroup$ – Petrus1904 Nov 18 '20 at 16:28
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For periodic signals you can use

$$P_y=\frac{1}{N}\sum_{n=0}^{N-1}|y[n]|^2\tag{1}$$

where $N$ is the period of the signal. I'm sure you can take it from here.

Also take a look at this question and its answer where the equivalence of $(1)$ and the formula in your question is discussed.

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