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Integrating seperable equation

  1. Sep 21, 2008 #1
    1. The problem statement, all variables and given/known data

    Separable equations

    dy/dx = y * e^(sinx +cosy)

    and

    dy/dx = sin(x^y)

    3. The attempt at a solution

    For the first problem, I did dy/dx = y * e^(sinx) * e^(cosy) and separated. However, I can't figure out how to integrate e^(sinx)dx on the right. Did I do somehting wrong?

    I have no idea what to do on the second one



    Thanks for the help!
     
    Last edited: Sep 22, 2008
  2. jcsd
  3. Sep 22, 2008 #2
    Help pleeeease
     
  4. Sep 24, 2008 #3

    Gib Z

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    For the first one, my first impression would have been to let u= sin x, giving [tex]\int \frac{e^u}{\sqrt{1-u^2}} du [/tex] and then tried an integration by parts. Checking with the Integrator online however, it seems there is no elementary antiderivative for that function, so don't be surprised if the Integration by parts doesn't work out. Still try it though, because the Integrator has been wrong before.

    The Second one isn't actually separable.
     
  5. Sep 24, 2008 #4

    HallsofIvy

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    Staff Emeritus
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    The second, y'= sin(x^y), is NOT separable.

    The first is separable but gives integrals that cannot be integrated as elementary functions.
    [tex]\int \frac{dy}{ye^{cos(y)}}= \int e^{sin(x)} dx[/tex]
    is the best you can do.

    Thanks, Gib Z.
     
    Last edited: Sep 24, 2008
  6. Sep 24, 2008 #5

    Gib Z

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    Small correction - The exponential term on the LHS should be in the denominator. =]
     
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