Calculating sup, inf, limsup, liminf, and limit points of a sequence

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SUMMARY

The discussion focuses on calculating the supremum (sup), infimum (inf), limit superior (limsup), limit inferior (liminf), and limit points of the sequence defined by x_n = 1/n + (-1)^n. The correct values determined are: limsup = 1, liminf = -1, sup = 1.5, and inf = -1. The method of analyzing the sequence by writing out the first few terms to observe trends is validated, and the user is advised that their initial assumption about inf was incorrect.

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*melinda*
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Question:
(I've got a few like this, so I'd like to know if I am doing them correctly.)

Compute the sup, inf, limsup, liminf, and all the limit points of the following sequence x_1, x_2,... where

x_n = 1/n + (-1)^n

What I did was write down the first few terms to get an idea of the behavior of the sequence.
From this I found that the limit points were 1 and -1
limsup = 1
liminf = -1
sup = 1.5 (I think)
inf = 0 (I'm not sure)

I'm not so sure about the inf because I don't think inf = liminf is allowed, but in this case the lower endpoint and the liminf both equal -1, I think...

Did I determined these values by the correct method, or is there some formal way of which I am unaware to 'compute' these things?

Also, are my values correct?

thanks-a-bunch :smile:
 
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write out the first few terms of the sequence and watch the trend of the terms. Your inf is wrong. Your sup is fine.
 
So that would mean that my inf = -1, just like I thought it should be. :rolleyes:

Thanks a lot!
 

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