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-   -   Solution for a logarithmic equation (https://www.askmehelpdesk.com/showthread.php?t=340172)

  • Apr 11, 2009, 06:02 AM
    Dashone
    solution for a logarithmic equation
    How would one solve the following for x?
    y=ln(x+1)+x
  • Apr 11, 2009, 09:52 AM
    galactus
    There is no nice algebraic way to solve this for x.
  • Apr 11, 2009, 10:55 AM
    Dashone
    Galactus,
    I did not think there was an "easy" algebraic solution. I guess what I am really asking is what numerical method could be used if I alread know the values for y?
  • Apr 11, 2009, 01:33 PM
    galactus
    OK. If we have a y value, let's use Newton's method.

    That is always a good standby.

    Let's say y=3.





    Find the derivative:

    Newton's method is

    Start with an initial guess of, say, 1.5:



    Do it again:



    Keep doing it until it converges close enough.

    The actual solution is 1.92627106244. So we are very close.
  • Apr 11, 2009, 04:01 PM
    Dashone

    THANKS GALACTUS! I new there was some method, it was just escaping me.

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