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Homework Help: Natural log derivative problem

  1. Sep 14, 2005 #1
    Hello all. I am stuck on this homework problem. It wants me to find
    [tex]
    \frac {d^2y} {dx^2}
    [/tex]
    when [tex] y= ln x^8 [/tex]
    The book answer is [tex] \frac {-8}{x^2}[/tex]
    But I only can get [tex] \frac {-8}{x^9)}[/tex]

    Please give me some guidance
    Thanks
     
    Last edited: Sep 14, 2005
  2. jcsd
  3. Sep 14, 2005 #2

    saltydog

    User Avatar
    Science Advisor
    Homework Helper

    Need to keep very clear the precedence of operators so write it as:

    [tex]y=ln(x^8)[/tex]

    Now, just differentiate once to get 8/x, one more time to get the book's answer.
     
  4. Sep 14, 2005 #3
    Thx so much
     
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