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Homework Help: Help I Need To Find The Derivative

  1. Jul 26, 2008 #1
    Help I Need To Find The Derivative!!!

    I don't know how to find the derivative of cos(8theta)

    i know there is an identity cos(2theta) but idk if I am able to expand it or not?
     
  2. jcsd
  3. Jul 26, 2008 #2

    nicksauce

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    Re: Help I Need To Find The Derivative!!!

    Are you familiar with the chain rule?
     
  4. Jul 26, 2008 #3
    Re: Help I Need To Find The Derivative!!!

    Just make 8theta a function, then use the general power, or chain rule to differentiate. in other words you want to find dy/dtheta. So using the general power rule, or chain rule, the derivative=-sin(8theta)*(8theta')=-8sin(8theta)
     
  5. Jul 26, 2008 #4

    HallsofIvy

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    Re: Help I Need To Find The Derivative!!!

    nicksauce and poopcaboose are both saying that you don't need to expand it at all- just use the chain rule.
     
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