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May 5th, 2018, 03:00 PM   #11
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Originally Posted by Kavesat View Post
Thanks for reply, sir. Yes, I have learned some lim like this.

Sorry, I can't totally understand what you mean about Σ.
If the following Σ is right, why can't you directly replace the k with cos(k) and then calculate?

if you can replace, the value will go down - then go up + between -1 and 1...They will neutralize each other.
You can of course compute the various cos(k) and add them up to get approximate numeric values. That does not necessarily mean that the sums can be condensed into a simple expression, a so-called closed form.

No, the sums do not neutralize each other, whatever that means. It is true that the various sums oscillate and are sometimes positive and sometimes non-positive, but the oscillation continues forever. It doesn't get to zero and then stay there.
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