Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help: logarithmic equation

  1. Sep 21, 2004 #1
    Hi everyone. I'm new in the forum and I'd need an help to solve this equation (sorry, I think it's quite easy but I'm not an expert of mathematics..):

    a*x + b*ln(x) = c

    where a, b, c are parameters and I need to find the value of x.

    Do I need to use techniques of differential equations?

    Thanks a lot for any help.
  2. jcsd
  3. Sep 21, 2004 #2
    You need to use Numerical Techniques.
    Have u come across Newton Raphson method ? It should do just fine on this one.

    -- AI
  4. Sep 21, 2004 #3
    No, I've never used the Newton Raphson method.. thanks, i'll have a look to this technique, however, I suppose I need to use some maths softwares to compute the result, isn't it?
  5. Sep 21, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No. Any scientific calculator will work. You could also use Excel, if you choose.

    Hopefully, you won't have to go through too many iterations.
  6. Sep 21, 2004 #5


    User Avatar
    Science Advisor

    There is also the "Lambert's W" function. It is defined specifically as "W(x) is the y satisfying yey= x". In other words, it is the inverse of the function xex.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook