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Homework Help: Trouble finding the derivative

  1. Oct 9, 2006 #1
    Hi

    I'm having trouble finding the derivative of this function.

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

    This is what I've tried so far, but I seem to be getting nowhere.
     

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  3. Oct 9, 2006 #2

    arildno

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    Hi raul!
    The nasty part of this is, of course the logarithm part, and possibly rearranging the expression you get afterwards.

    For starters:
    What is the derivative wrt. x of [itex]\sqrt{1+x^{2}}[/itex]?
     
  4. Oct 9, 2006 #3
    [tex] -\frac{x}{\sqrt{1+x^2}} [/tex] ?
     
  5. Oct 9, 2006 #4

    arildno

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    Why the minus sign??
     
  6. Oct 9, 2006 #5
    Right, no minus sign there.. my bad.

    However, now I get [tex] \ln(x+\sqrt{1+x^2}) [/tex]
    Is this correct?
     

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