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

  • #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!
 

Answers and Replies

  • #2
Office_Shredder
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Can you find f'(3x4)?
 
  • #3
HallsofIvy
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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).
 

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