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January 29th, 2019, 01:02 PM   #11
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Quote:
 Originally Posted by zylo Good grief. Why all the contortions? By L'Hôpital's rule: lim log(1+2x)/x = lim 2/(1+2x) = 2
... because some profs do not allow the use of L'Hôpital.

ok, Zeke?

Last edited by skipjack; March 26th, 2019 at 12:41 AM.

January 29th, 2019, 07:25 PM   #12
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Quote:
 Originally Posted by skeeter ... because some profs do not allow the use of L'Hopital. ok, Zeke?
Why?

January 30th, 2019, 05:55 AM   #13
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Quote:
 Originally Posted by zylo Why?
math.stackexchange.com questions ... whats-wrong-with-lhopitals-rule?

January 30th, 2019, 06:24 AM   #14
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Quote:
 Originally Posted by skeeter math.stackexchange.com questions ... whats-wrong-with-lhopitals-rule?
So what?

1) You want OP to do it without L'hospital's rule for limit practice? Than say so.

2) It doesn't work sometimes? Sure, it may happen that you can't evaluate lim f'(x)/g'(x). But that doesn't mean it's wrong and you can't use it.

3) OP asked for limit. He didn't specify how to find it.

The response "you can't use it" implies there is something wrong with it and only you know what it is. Have you thought about a career in journalism slick?

 January 30th, 2019, 06:26 AM #15 Senior Member   Joined: Dec 2015 From: iPhone Posts: 479 Thanks: 73 Yes that is the reason. But in physics it is allowed to use it if it works. Last edited by idontknow; January 30th, 2019 at 06:33 AM.
January 30th, 2019, 06:55 AM   #16
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Quote:
 Originally Posted by zylo So what? 1) You want OP to do it without L'hospital's rule for limit practice? Than say so. 2) It doesn't work sometimes? Sure, it may happen that you can't evaluate lim f'(x)/g'(x). But that doesn't mean it's wrong and you can't use it. 3) OP asked for limit. He didn't specify how to find it. The response "you can't use it" implies there is something wrong with it and only you know what it is. Have you thought about a career in journalism slick?

Quote:
 ... because some profs do not allow the use of L'Hopital.

January 30th, 2019, 07:06 AM   #17
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Quote:
 Originally Posted by skeeter from here, I recommend using the series expansion about zero for $\ln(1+2x)$ , simplifying the resulting quotient, and then determine the limit.
The limit of an infinite sum of terms each one of which approaches zero is meaningless. Unless you know the sum for all x to begin with, ie, know what you are trying to prove, or can prove convergence of the limit.

Ok, zeke?

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