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Calculating value of f'(x)

  1. Nov 21, 2009 #1
    1. The problem statement, all variables and given/known data
    [f(x)]^5 + f(x)/(7x^2)=4
    when f(2)=3, calculate f'(2)


    2. Relevant equations



    3. The attempt at a solution
    Attachment has solution

    I am stuck. I don't know if I am right upto there.
     

    Attached Files:

  2. jcsd
  3. Nov 21, 2009 #2

    Dick

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    Science Advisor
    Homework Helper

    I can't see your attachment. But just take the derivative of both sides of the equation and solve for f'(x).
     
  4. Nov 22, 2009 #3

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Here is what is in the attachment:
    That has a sign wrong- either drop the parentheses or write
    [tex]f'(x)= 56x- (14x\left[f(x)\right]^5+ 35x^2\left[f(x)\right]^4 f'(x))[/tex]

    and you now have the sign right!

    Now, just solve for f'(2): add 11340f'(2) to both sides and divide by 11341.
    (I didn't check your arithmetic!)
     
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