Question about the comparison test

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Homework Help Overview

The discussion revolves around determining the convergence or divergence of the series (∞,n=1) ∑ (n² - 1)/(3n⁴ + 1), which falls under the topic of series convergence tests in calculus.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the choice of comparison series and the limit of the ratio of terms. There is uncertainty about the direction of the approach and the calculation of the limit.

Discussion Status

The discussion is ongoing, with participants exploring the limit of the ratio of terms and questioning the validity of their approaches. Some guidance has been offered regarding the choice of the comparison series.

Contextual Notes

There is a focus on the limit as n approaches infinity, with participants expressing difficulty in reaching a conclusion about the series' behavior.

vande060
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Homework Statement



determine whether the series diverges or converges

(∞,n=1) ∑ (n2 - 1)/(3n4 +1)

Homework Equations


The Attempt at a Solution



(∞,n=1) ∑ (n2 - 1)/(3n4 +1)

an = (n2 - 1)/(3n4 +1)

i thought bn should be n2/3n4 = 1/3n2

lim n-->∞ an/bn = (n2 - 1)/(3n4 +1) * 3n2

lim n-->∞ (3n4 - 3n2)/ (3n4 + 1)

not sure if this is going in the right direction here
 
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vande060 said:

Homework Statement



determine whether the series diverges or converges

(∞,n=1) ∑ (n2 - 1)/(3n4 +1)



Homework Equations





The Attempt at a Solution



(∞,n=1) ∑ (n2 - 1)/(3n4 +1)

an = (n2 - 1)/(3n4 +1)

i thought bn should be n2/3n4 = 1/3n2
That's a reasonable choice.
vande060 said:
lim n-->∞ an/bn = (n2 - 1)/(3n4 +1) * 3n2

lim n-->∞ (3n4 - 3n2)/ (3n4 + 1)

not sure if this is going in the right direction here
So what do you get when you take the limit?
 
Mark44 said:
So what do you get when you take the limit?

thats where i kept getting bogged down, let me give it another shot:

lim n-->∞ (3n4 - 3n2)/ (3n4 + 1)

lim n-->∞ (3 - 3/n2)/ (3 + 1/n4)

im n-->∞ = 1

c>0, series converges
 

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