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Math Beauty and Her Limits

by marlen
Tags: beauty, limits, math
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Nov1-07, 08:00 PM
P: 16

Can someone please help me prove that

the lim as n goes to infinity of (the sequence an + the sequence bn) = (the lim of an) + (the lim of bn).

What I think is that if one adds the two limits an + bn, she will come up with a new sequence cn and take its limit, which equals L. Then if she takes the limit of an and set it equal to L1 and take the limit of bn and set it equal to L2...

After this I don't know. I don't even know if this makes sense. Someone please help me!

I hope all of this makes sense. :)
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Nov1-07, 09:17 PM
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EnumaElish's Avatar
P: 2,481
1. Since cn ---> L, there must be a relationship between the elements of cn and the number L. State that relationship.

2. Now you need to show that the relationship stated in "1" indeed holds. To show this:

a. assume L = L1 + L2

b. use the given fact that the relationship stated in "1" holds between an and L1, as well as between bn and L2, to show that when L = L1 + L2, the relationship in "1" holds between cn and L.
Nov2-07, 12:44 PM
P: 176
you could use the epsilon-N definition to show it too. it's a pretty straightforward application of the triangle inequality.

Nov3-07, 06:35 AM
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PF Gold
P: 39,689
Math Beauty and Her Limits

You will also want to use [itex]|a+ b|\le |a|+ |b|[/itex].

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