1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Natural logs

  1. Jun 16, 2006 #1
    just wanted to know how i would differentiate y = ln(x^2 - 1)^3x

    i thought id first bring the 3x out in front and then do product rule but i dont think that yielded the right answer (i dont know the right answer btw but it didnt look right)

    y' = 3 ln(x^2-1) + 6x^2/(x^2-1)
     
  2. jcsd
  3. Jun 16, 2006 #2

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Your method is correct as is your answer. Why do you say that it doesn't look right?
     
  4. Jun 16, 2006 #3
    is that the most simplified form?

    i graphed the original function using some graphing software and automatically found what the derivative graph is supposed to look like. i then graphed the derivative i found and they did not match (two different functions). maybe i just entered it incorrectly, the graphing software is extremely picky about order of operations, brackets and all that...
     
    Last edited: Jun 16, 2006
  5. Jun 16, 2006 #4

    StatusX

    User Avatar
    Homework Helper

    Is that suppposed to be:

    [tex]y=(\ln(x^2+1))^{3x}[/tex]

    ? If so, its probably easiest to take the ln again, so you get:

    [tex]\ln(y)=3x\ln(\ln(x^2+1))[/tex]

    And then differentiate both sides, using the chain rule on the RHS, and then solve for dy/dx (plug back in for y).
     
    Last edited: Jun 16, 2006
  6. Jun 16, 2006 #5

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I would consider that the most simplified form. Well, I differentiated by hand, then integrated to check it and arrived at the original solution. Are you sure you entered the correct function in you software? (I used the same method as you btw)
     
  7. Jun 16, 2006 #6
    StatusX: yes that is correct function. i doubt we had to do the method you described simply because we really never did any like that in class.

    Hootenanny: hey now ive got it! i tried a few variations. i had to enter the original function like this y = ln((x^2 - 1)^(3x)) - i hope thats still the same function...
     
  8. Jun 16, 2006 #7

    StatusX

    User Avatar
    Homework Helper

    I edited the post, but it appears it wasn't the function I thought. In that case, yes, your method and answer are correct.
     
  9. Jun 16, 2006 #8

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes thats the same function;

    [tex]y = \ln\left|(x^2 - 1)^{3x}\right|[/tex]

    You have to be careful when entering functions into your computer of calculator, if in doubt use brackets and plenty of them!:tongue:
     
    Last edited: Jun 16, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Natural logs
  1. Natural Log (Replies: 4)

  2. Natural log of product (Replies: 2)

Loading...