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Quick question about a small problem

  1. Apr 8, 2014 #1
    1. The problem statement, all variables and given/known data

    In my work I am stuck at this equation:
    [itex]840+1.5v^{2.4}-3.6v^{1.4}=0[/itex]

    I am looking for a quick, easy way to solve this.
    Any suggestions? I am kinda tired right now and nothing comes to my mind except maybe Newtons method?
     
  2. jcsd
  3. Apr 8, 2014 #2
    Okay, so this equation comes from the derivative of

    [itex]s(x)=\frac{600v}{1.4+0.0025*v^{2.4}}[/itex]

    But Wolfram Alpha tells me the derivative is wrong? Oo
    What did I do wrong?

    [itex]s'(x)=\frac{600(1.4+0.0025v^{2.4})-600v(0.006v^{1.4})}{(1.4+0.0025*v^{2.4})^{2}}[/itex]

    [itex]s'(x)=\frac{840+1.5v^{2.4}-3.6v^{1.4}}{(1.4+0.0025*v^{2.4})^{2}}[/itex]
     
    Last edited: Apr 8, 2014
  4. Apr 8, 2014 #3

    Ray Vickson

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    ##v \times v^{1.4} = v^{2.4}##, not ##v^{1.4}##.
     
  5. Apr 8, 2014 #4

    Ray Vickson

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    A simple plot of ##840+1.5v^{2.4}-3.6v^{1.4}## shows that the equation has no positive real roots and hence has no real roots at all.
     
  6. Apr 8, 2014 #5
    Thanks, I overlooked the v
     
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