Limit of [x^2(3 + sinx)] / [(x + sinx)^2]

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Homework Help Overview

The discussion revolves around evaluating the limit of the expression [x^2(3 + sinx)] / [(x + sinx)^2] as x approaches 0, within the context of introductory calculus.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss expanding the expression and the challenges faced when substituting x = 0, leading to a zero denominator. Suggestions include using series expansion or factoring out terms to simplify the limit evaluation.

Discussion Status

The conversation is ongoing, with participants exploring various methods to approach the limit. Some guidance has been offered regarding factoring and series expansion, but no consensus has been reached on a definitive method.

Contextual Notes

It is noted that the problem is intended for an introductory Calculus 1 course, which limits the use of certain techniques such as l'Hopital's rule.

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Homework Statement


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The Attempt at a Solution



I expanded everything out and got [3x^2 + x^2*sin(x)] / [x^2 + 2sin(x) + sin^2(x)] and I tried splitting the problem but it didn't work because the denominator is always 0 when I try plugging in '0' for 'x.' I can't find any way to cancel out the denominator
 
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You can't really 'cancel out' the denominator. You could try l'Hopital's rule or substituting a series expansion of sin(x). Or factoring x^2 out of the denominator and using a known limit like sin(x)/x.
 
Oops, sorry, I forgot to mention this is for an introductory Calc 1 course, so none of that l'Hopital stuff...

But what do you mean about substituting a series expansion?
 
PhizKid said:
Oops, sorry, I forgot to mention this is for an introductory Calc 1 course, so none of that l'Hopital stuff...

But what do you mean about substituting a series expansion?

I think my last suggestion about factoring x^2 out of the denominator is the best. I added that to my post in an edit. Try that.
 
So then I get:

[x^2(3 + sinx)] / [x^2(1 + 2sinx/x + sin^2x/x] and cancel out the x^2's:

(3 + sinx) / (1 + 2sinx/x + sin^2x/x)

Editl: Oh, I had made an algebra error. I got it now, thanks
 

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