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

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In summary, the conversation is about solving a problem involving a complex fraction with a denominator that becomes zero when 'x' is plugged in as 0. Suggestions are made to use l'Hopital's rule or a series expansion, but it is clarified that these may not be applicable for an introductory Calc 1 course. Instead, it is suggested to factor out x^2 from the denominator and use a known limit. After making an algebra error, the problem is successfully solved.
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PhizKid
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Homework Statement


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Homework Equations





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.
 
  • #3
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?
 
  • #4
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.
 
  • #5
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
 

What is the limit of the function as x approaches infinity?

The limit of the function as x approaches infinity is 3. This is because as x gets larger and larger, the term x^2 becomes much larger than the sine term and therefore the function behaves like 3/x^2 which approaches 0 as x approaches infinity.

What is the limit of the function as x approaches 0?

The limit of the function as x approaches 0 is 1. This is because as x approaches 0, the term sinx becomes negligible compared to x^2 and the function behaves like x^2/x^2 which simplifies to 1.

Is the function continuous at x=0?

Yes, the function is continuous at x=0. This is because the limit of the function as x approaches 0 is equal to the value of the function at x=0, which is 1. Therefore, there are no "jumps" or breaks in the graph of the function at x=0 and it is continuous.

What is the behavior of the function as x approaches values close to pi?

The function approaches positive infinity as x approaches values close to pi. This is because as x gets closer to pi, the sine term approaches 1 and the numerator becomes much larger than the denominator, causing the function to approach positive infinity.

What is the behavior of the function as x approaches values close to -pi?

The function approaches negative infinity as x approaches values close to -pi. This is because as x gets closer to -pi, the sine term approaches -1 and the numerator becomes much larger than the denominator, causing the function to approach negative infinity.

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