View Full Version : Derivative for ln(x)
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.