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!

Calculate f'(x) given d/dx(f(3x^4))=6x^4?

  1. Sep 21, 2010 #1
    I am told that d/dx(f(3x^4))=6x^4. I need to calculate f ' (x). i have tried like 3 different methods and have no idea how to do this.
    Help please!
  2. jcsd
  3. Sep 21, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Can you find f'(3x4)?
  4. Sep 22, 2010 #3


    User Avatar
    Science Advisor

    By the chain rule,
    [tex]\frac{df(3x^4)}{dx}= f'(3x^4)(12x^3)[/tex]

    So you must have [itex]f'(3x^4)(12x^3)= 6x^4[/itex].

    That lets you find [itex]f'(3x^4)[/itex] per Office Shredder's question. Now, if you let [itex]u= 3x^4[/itex], you can find f'(u).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook