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Homework Help: Partial derivative question.

  1. Feb 26, 2012 #1
    1. The problem statement, all variables and given/known data
    I can't seem to find information on this specific question i have.

    So i'm taking the partial derivative of this equation for both x and y
    I know how to do it for y, but I am not seeing something with respect to x
    fx(x,y)= x^7 + 2^y + x^y

    2. Relevant equations

    3. The attempt at a solution

    So this is what I thought it should be

    7x^6 + 1 + yx^(y-1)

    I guess the answer is 7x^6+yx^(y-1) according to cramster and there is no 1 in it.

    Why does 2^y not go to 1?

    I would think because you treat y as a constant that it would go to zero and 2^0 is 1
    What is wrong with my reasoning?

    Thanks for reading
  2. jcsd
  3. Feb 26, 2012 #2


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    If you treat y as a constant, then 2y is also a constant.
  4. Feb 27, 2012 #3


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    Have you considered using the identity:

    a^b =e^{bloga} ?
  5. Feb 27, 2012 #4


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    First, stop even thinking Z"it goes to"! That is too vague and you are confusing yourself. The derivative of a constant is 0 but that does NOT mean that y itself is 0.

    [/quote]Thanks for reading[/QUOTE]
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