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pop000
Dec 30, 2010, 04:44 AM
How do I find the Derivative for the Function.


Thanks.

ebaines
Dec 30, 2010, 12:39 PM
The derivative of ln(x) is 1/x. I'm not sure what you're trying to get at with your formula:


\ln(x) = - \frac 1 {x-1}


This formula is incorrect, so please clarify your question.

pop000
Dec 30, 2010, 01:59 PM
hi. I know that the derivative of ln(x) is 1/x. but the original question was to prove that the Function ln(x)=1/x-1 has exactly 2 Solutions

I need to find the derivative.


hope is more clear now :)

galactus
Dec 30, 2010, 03:16 PM
You can use the Intermediate Value Theorem and/or Rolles Theorem to prove it has two solutions.

harum
Dec 30, 2010, 09:40 PM
Would like to help you but have not a slightest idea what you want to do here.

Equations ln(x) = 1/x-1 and ln(x) = -1/(x-1) are not the same, so it gets more and more confusing.

The first equation has only one solution, the second -- none.

galactus
Dec 31, 2010, 04:54 AM
You can rewrite it as:

ln(x)+\frac{1}{x-1} and then try to show this has exactly two solutions.

The thing is, it does not have two solutions.

But, if it were ln(x)=\frac{1}{x-1}\Rightarrow ln(x)-\frac{1}{x-1}, then it would have the two solutions.

Both graphs appear below.

pop000
Jan 1, 2011, 03:23 AM
OK I will try thanks to all of you for helping.