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Derivative Problem! Please help

  1. Jun 3, 2009 #1
    1. The problem statement, all variables and given/known data

    Let F(x)= f(x^8) and G(x)=(f(x))^8. You also know that a^7= 14, f(a)=2, f'(a)= 10, f'(a^8)=4 Find F'(a)=______ and G'(a)=______


    2. Relevant equations



    3. The attempt at a solution

    G(a)=(f(a))^8
    G'(a)=8(f(a))^7*(f'(a))
    G'(a)=8(2)^7*10
    G'(a)=10240

    F(a)=f(a^8)
    F'(a)=k(f'(a))
    F'(a)=1*(4)
    F'(a)=4

    One of the two is incorrect but I do not know which one and I am am not sure how to go about finding it
     
  2. jcsd
  3. Jun 3, 2009 #2

    Cyosis

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    Sorry for being suspicious, but are these your own attempts at a solution? I find it hard to believe that you can do one correctly and completely miss the other. What is k?
     
  4. Jun 3, 2009 #3
    Yes they're my own attempts. The reason I don't know why I'm missing one of them is cause I don't see anything wrong! Which is why i'm looking for help. And k is the sign for constant
     
  5. Jun 3, 2009 #4

    Cyosis

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    How does that constant end up there? There is not a single k to be found anywhere else in your problem. Either way apply the chain rule in the same way as you did with G.
     
    Last edited: Jun 3, 2009
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