1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    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


    User Avatar
    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!)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook