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I have this limit:

$$\lim_{x \to 1} \frac{2x^2-x-6}{x(x-1)^3}$$

This can be written as:

$$\lim_{x \to 1^+} \approx \frac{-5}{1\times\mbox{tiny positive}} \to - \infty$$

Why is that? I mean, let's plug in some numbers. $-5/1.0000000001$ is almost $-5$ , the greater the denominator becomes the close the number to $-5$

Can anybody tell me why the book says it goes to -infinity? Thanks a lot

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    Your post was edited for better readability. You should check, whether everything is ok. You should also choose between $n$ and $x$ - I guess they denote the same thing. (This problem was already in your original post, before the edit.)2011-11-11
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    Believe it or not, text book writers sometimes make mistakes...2011-11-11
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    Indeed, I didn't change any *variables*, but did try to make it more readable! @Martin2011-11-11
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    But more to the point, the limit is indeed equal to $-5$, as you can check for yourself: http://www.wolframalpha.com/input/?i=limit+x+to+1+%282x%5E2-x-6%29%2F%28x-%28x-1%29%5E3%292011-11-11
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    It was a typo. The denominator is actually x(x-1)^3 not x-(x-1)^3. So now it's clear why it goes to infinity.2011-11-11
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    Well, you still have $n$'s in the limit, but we get what you mean :)2011-11-11
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    I had added a comment that the limit is $-5$. But the function has now changed. There is still the $n$ versus $x$ problem. With the changed function, $\lim_{x\to 1^+}$ is $-\infty$. If we approach from the other direction, limit is $\infty$. So there is no such thing, even in the extended sense, as $\lim_{x \to 1}$.2011-11-11
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    Ok... would the **next** person to edit this change the $n$'s to $x$'s ?!?!?2011-11-11
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    I made the change but my edit needs to be OP approved.2011-11-11

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You didn't choose a tiny positive number! Rather than $1.00000000001$, you should have chosen $0.0000000000001$


One benefit of choosing such tiny decimal numbers is that we can represent them as fractions. So we would get fractions $\frac{1}{1000} , \frac{1}{10000000} , \frac{1}{100000000000} $ ,etc.

But dividing by these fractions is the same as multiplying by $1000, 10000000, 100000000000$, etc. The effect of this is that the fraction grows arbitrarily large.

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    Thanks a lot. It makes sense now2011-11-11
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    Glad to help! .2011-11-11