What is the Limit as n Approaches Infinity of a Rational Function?

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Homework Help Overview

The discussion revolves around finding the limit of a rational function as n approaches infinity, specifically the expression (n+1)^2 / (√3 + 5n^2 + 4n^4). Participants are exploring the behavior of the function as n increases and the implications of dividing by n^4.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants suggest dividing both the numerator and denominator by n^4 to simplify the limit calculation. There are questions about the correct interpretation of the denominator, particularly whether the terms are under a radical or not. Some express confusion about how to handle the radical when dividing by n^4.

Discussion Status

The discussion is active, with participants providing different approaches to simplify the limit expression. Some have offered guidance on how to manipulate the radical and the terms involved, while others are still clarifying their understanding of the setup and simplification process.

Contextual Notes

There is a noted difficulty in simplifying the radical expression, and participants are working through the implications of dividing by n^4 and how it affects the limit. The original poster indicates uncertainty about the correct form of the denominator, which is crucial for the limit evaluation.

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Homework Statement



Find limit as n -> infinity

[ (n+1)^2 ] / [ \sqrt{}3+5n^2+4n^4 ]

Homework Equations



L'Hopital won't do the job, I think.

The Attempt at a Solution



It's something really small I'm just completely missing.
 
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divide the numerator and denominator by n^4
 
ircdan said:
divide the numerator and denominator by n^4

I found an example that said exactly that, but I guess I don't see clearly how, first of all,

the radical / n^4 comes out pretty.
 
you have, (n+1)^2/(sqrt(3) + 5n^2 + 4n^4), or

(n^2 + 2n + 1)/(sqrt(3) + 5n^2 + 4n^4), so dividing num and denom by n^4,

(1/n^2 + 2/n^3 + 1/n^4)/(sqrt(3)/n^4 + 5/n^2 + 4) and now the limit as n->inf is ...
 
ircdan said:
you have, (n+1)^2/(sqrt(3) + 5n^2 + 4n^4), or

(n^2 + 2n + 1)/(sqrt(3) + 5n^2 + 4n^4), so dividing num and denom by n^4,

(1/n^2 + 2/n^3 + 1/n^4)/(sqrt(3)/n^4 + 5/n^2 + 4) and now the limit as n->inf is ...

Oh, I'm sorry. In the denominator, everything is actually under the radical. It doesn't matter, however, because the numerator comes out to zero. Thanks for the help.
 
\sqrt{3}+5n^2+4n^4 OR \sqrt{3+5n^2+4n^4} ?

if the last one, then divide num and denom by n^2
 
Last edited:
jdg812 said:
\sqrt{3}+5n^2+4n^4 OR \sqrt{3+5n^2+4n^4} ?

if the last one, then divide num and denom by n^2

It's the last one, everything under the radical.

My problem is I'm not seeing how I would divide something like

\sqrt{3+5n^2+4n^4} / n^4, or / any number, for that matter. I'm not seeing how to simplify that radical into individual terms.
 
dalarev said:
It's the last one, everything under the radical.

My problem is I'm not seeing how I would divide something like

\sqrt{3+5n^2+4n^4} / n^4, or / any number, for that matter. I'm not seeing how to simplify that radical into individual terms.
You should not simplify the radical, just put n^2 INSIDE the radical... and remember that n^2 becomes n^4 when inside radical...
 
dalarev said:
It's the last one, everything under the radical.

My problem is I'm not seeing how I would divide something like

\sqrt{3+5n^2+4n^4} / n^4, or / any number, for that matter. I'm not seeing how to simplify that radical into individual terms.

figured this would be your difficulty, here is an example
sqrt(n^2 + 2n)/n^2 = sqrt(n^2 + 2n)/sqrt(n^4) = sqrt((n^2 + 2n)/n^4) = sqrt(1/n^2 + 2/n^3)

try to see why it works, now mimic it for your problem.
 
  • #10
Ahh, I see it. I forgot about that property where you're allowed to simply "take out" multiplying/dividing terms. I see it now, thanks a bunch.
 

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