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    Hey

    Please could you tell me what's wrong with this:
    I have the solutionbank and there's a different answer there.
    Thanks

    EDIT: solved !
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    What is the question?
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    (Original post by steve2005)
    What is the question?
    Differentiate with respect to x :

    ln \frac{1}{x^2 + 9}
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    (Original post by Limoncello)
    Differentiate with respect to x :

    ln \frac{1}{x^2 + 9}
    Oh. That's a 9? Damnit. When I post my answer, substitute 9 for g, lol. I've been doing too much mechanics.
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    (Original post by Limoncello)
    Hey

    Please could you tell me what's wrong with this:
    I have the solutionbank and there's a different answer there.
    Thanks
    You can split your original function into two logs by observing that ln(\frac{a}{b}) = ln(a)-ln(b).
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    Name:  Ln.JPG
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Size:  78.3 KB

    Basically, the only thing you've really misinterpreted is how to use the reciprocal as a power, rather than having that nasty double fraction.

    I would personally use Method 1.
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    (Original post by EEngWillow)
    You can split your original function into two logs by observing that ln(\frac{a}{b}) = ln(a)-ln(b).
    Thanks !
    I knew that way. that's the one in the solution bank.
    I just wanted to know why this one was wrong.
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    (Original post by TwilightKnight)
    Name:  Ln.JPG
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    Basically, the only thing you've really misinterpreted is how to use the reciprocal as a power, rather than having that nasty double fraction.

    I would personally use Method 1.
    Thank you very much for taking the time to do it, scan it and upload it
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    (Original post by Limoncello)
    Thank you very much for taking the time to do it, scan it and upload it
    Lol. No worries. I just wish I'd seen the thread sooner :P.

    As a heads up, if you end up doing M3-M5, you'll get used to differentiating and integrating (usually by parts or substitution) reciprocal logs (i.e, variable mass questions, resisted motion questions). They don't turn up that much in C3 and C4, which makes them a little surprising when you first come across them in Mechanics.
 
 
 
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