What is the limit of 1/n^2 + 2/n^2 + + n-1/n^2 as n-> infinity

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Homework Help Overview

The problem involves finding the limit of the sum \( \frac{1}{n^2} + \frac{2}{n^2} + \frac{3}{n^2} + \ldots + \frac{n-1}{n^2} \) as \( n \) approaches infinity, which falls under the topic of limits and series in calculus.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the limit's value, with some suggesting it might be zero while others challenge this assumption. There is an exploration of expressing the sum in closed form and clarifying the type of series involved.

Discussion Status

The discussion is active, with participants sharing their reasoning and attempting to clarify concepts. Some guidance has been provided regarding the summation formula for arithmetic series, and there is an ongoing exploration of the implications of this formula for the limit.

Contextual Notes

There is some confusion regarding the terminology used, particularly around "closed form" and the nature of the series (arithmetic vs. geometric). Participants are also navigating the correctness of their approaches and interpretations of previous contributions.

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Homework Statement



find:

lim(n[tex]\rightarrow\infty[/tex] (1/n^2 + 2/n^2 + 3/n^2 + ... + n-1/n^2 )

Homework Equations





3. The Attempt at a Solution [/b

I could guess that the limit is zero but i don't know howto prove it
 
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sara_87 said:

Homework Statement



find:

lim(n[tex]\rightarrow\infty[/tex] (1/n^2 + 2/n^2 + 3/n^2 + ... + n-1/n^2 )

Homework Equations





3. The Attempt at a Solution [/b

I could guess that the limit is zero but i don't know howto prove it

No, the limit is not 0.

That sum is the same as (1/n2)(1+ 2+ 3+ ...+ (n-1)). Can you write that last sum in closed form?
 


Oh right,
so, this is the same as:

[tex]\frac{1}{n^2}[/tex][tex]\sumk[/tex] (from k=1 to n-1)

and now i use the formula for geometric series?
 


Dick asked whether you knew a formula for 1 + 2 + 3 + ... + (n - 1). This is not a geometric series.
 


What is meant by 'closed form' ? i don't know, i thought dick meant that i should put it in a summation.
i meant arithmetic...sorry, surely this is not geometric.
 


I have done it and i just want to make sure of my answer:
i used the summation formula for aritmetic series :1/2 n(n+1)
and got that the limit is 1/2
is that right?
 


sara_87 said:
I have done it and i just want to make sure of my answer:
i used the summation formula for aritmetic series :1/2 n(n+1)
and got that the limit is 1/2
is that right?

Sure it's right. You could also look at the problem as being a Riemann sum for the integral of f(x)=x from x=0 to x=1. Surely, 1/2. BTW, I didn't say anything before in this thread. That was Halls. Let's give credit where credit is due.
 


Dick said:
BTW, I didn't say anything before in this thread. That was Halls. Let's give credit where credit is due.

Sorry for giving credit where not due. I think I saw your name in another thread that sara started, and mistakenly cited you and Dirk.
 


Mark44 said:
Sorry for giving credit where not due. I think I saw your name in another thread that sara started, and mistakenly cited you and Dirk.

No problem. If Hall's suggestion had been wrong, I would have been OUTRAGED to have it attributed to me. But it wasn't. :)
 

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