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Homework Help: Derivatives of trigonometric functions

  1. Jul 28, 2008 #1
    1. The problem statement, all variables and given/known data
    I'm learning now about darivative all by my self (without a teacher) and I'm not sure about this development

    2. Relevant equations

    3. The attempt at a solution



    [tex]{\Delta}Y=senx*cos{\Delta}x+ sen{\Delta}x*cosx[/tex]

    What about this cos,what is it doing in the equation?
    I really don't get it.
  2. jcsd
  3. Jul 28, 2008 #2
    Re: Derivative

    this comes from the double angle formula.

    it says that: sin (A + B) = sinAcosB + sinBcosA

    you can find the same thing for sin (x + dY)
  4. Jul 28, 2008 #3
    Re: Derivative

    Oh,now I think i get it!
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