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Differentiate f(x)= x sin x

  1. Jan 25, 2012 #1
    1. The problem statement, all variables and given/known data

    differentiate f(x)= x sin x

    2. Relevant equations



    3. The attempt at a solution

    The answer is x cos x + (sin x) * 1

    I thought the derivative of sine was cosine. So why isn't the answer x cos x?
     
  2. jcsd
  3. Jan 25, 2012 #2
    Don't forget about the [strike]chain[/strike] product rule:

    d/dx f(x)*g(x) = f'(x)g(x) + f(x)g'(x)

    In this case: f(x) = sin x & g(x) = x


    @vela - thanks for the correction
     
    Last edited by a moderator: Jan 25, 2012
  4. Jan 25, 2012 #3

    vela

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    You mean the product rule, not the chain rule.
     
  5. Jan 25, 2012 #4
    good, i got it now, thanks
     
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