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Inverse of exponential function

  1. Sep 17, 2011 #1
    1. The problem statement, all variables and given/known data

    Give the inverse of this function

    N=f(L)=1816-8L

    The answer has to be filled in in Maple

    2. Relevant equations



    3. The attempt at a solution

    N=1816-8L

    16-8L=ln(N)/ln(18)

    -8L=(ln(N)/ln(18))-16

    L=-ln(N)/(8*ln(18))+2

    Is this correct?
    When i fill this in in maple it's incorrect.
    I've really no clue why it is wrong.
     
  2. jcsd
  3. Sep 17, 2011 #2

    ehild

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    L=-ln(N)/(8*ln(18))+2 is the same function as the original. Choose L the independent variable and N the dependent one. (Just exchange L and N).

    ehild
     
  4. Sep 17, 2011 #3

    Mentallic

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    Yes it's correct. What are you typing into maple exactly? Your syntax is probably slightly off.

    edit: Sorry I didn't notice that you forgot to swap your variables.
     
  5. Sep 17, 2011 #4
    thanks! It's also mentioned that it should be simplified as much as possible.

    Does that mean that the 8*LN(18) could be simplified to 8*LN(2*9) and more?
     
  6. Sep 17, 2011 #5

    Mentallic

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    It's as simple as it can get, unless you believe [itex]\ln{\frac{1}{x}}[/itex] is more simple than [itex]-\ln{x}[/itex] you shouldn't be changing anything.

    [itex]\ln{18}[/itex] is definitely more desirable than [itex]\ln{9\cdot2}[/itex] :wink:
     
  7. Sep 17, 2011 #6

    Ray Vickson

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    When I let Maple solve the equation for L it gives me exactly what you wrote. Why do you think Maple thinks it is incorrectÉ What type of error message are you receivingÉ

    That annoying É is actually a question mark, but when I type it in it gives me that accented E; that only seems to happen when I access this website through Google Chrome!

    RGV
     
  8. Sep 17, 2011 #7
    Well, this assignment was given in a little online test.
    The point is, that i can't see why the answer was wrong.
    I have 2 chances, so for the second change i will try to swap the variables.
     
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