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Homework Help: Simple Derivation giving me a headache.

  1. Jan 18, 2012 #1
    1. The problem statement, all variables and given/known data
    Deriving http://www4d.wolframalpha.com/Calculate/MSP/MSP20181a00e6i82g005gag00005gb4c7hic8g2i3hi?MSPStoreType=image/gif&s=57&w=79&h=43 [Broken]

    2. Relevant equations

    3. The attempt at a solution

    My attempt gives me:
    -48/(x^2-16)^2 + 192x^2/(x^2-16)^3 via product rule

    Wolfram alpha gives me this for an answer

    http://www4d.wolframalpha.com/Calculate/MSP/MSP40371a00e53i06h6352d000061574g9ehi6a9958?MSPStoreType=image/gif&s=15&w=224&h=48 [Broken]

    I can't seem to figure out how to match my answer with Wolfram, even though it's not a tough derivative. Am I maybe not simplifying enough?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jan 18, 2012 #2


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    Homework Helper

    A simple trick that you can use to see if your answer actually matches up is to let x be a transcendental number like [itex]\pi[/itex] in your answer, then in Wolfram's. Since we're dealing with rational coefficients and exponents throughout, there is no way they can match up unless the answers are algebraically equivalent. They do match up in this case.

    So it's just a matter of rearranging your equation. Try reexpressing -48/(x^2-16)^2 as [itex]-\frac{48(x^2 - 16)}{{(x^2 - 16)}^3}[/itex] for starters, then combine the numerators over a common denominator.
    Last edited by a moderator: May 5, 2017
  4. Jan 18, 2012 #3
    The answers are equivalent. In order to get it into the same form, you need to make a common denominator.
  5. Jan 18, 2012 #4
    Ahh I see it now, thanks so much guys. Simple mistake, maybe I need a break...
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