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Homework Help: Nonlinear DE reduction

  1. Jun 23, 2012 #1
    1. The problem statement, all variables and given/known data

    [itex]\ddot{y} = - \dot{y} - y -sin(y)[/itex]

    2. Relevant equations
    3. The attempt at a solution
    to reduce the order I need to find a solution y1. it seems to me the only obvious solution is y1 = 0 but i can't use this to do a reduction can i
  2. jcsd
  3. Jun 23, 2012 #2
    Hi sunrah! :smile:

    You should be able to reduce the given DE to first order by substituting [itex]\frac{dy}{dx}= t[/itex]
  4. Jun 23, 2012 #3
    indeed, thank you!
  5. Jun 23, 2012 #4

    I hope you didn't write [tex]\frac{d^2y}{dt^2} = t'[/tex] :wink:
  6. Jun 23, 2012 #5
    i used
    [itex]\frac{d^{2}y}{dx^{2}} = \frac{dt}{dx}\frac{dy}{dy} = t\frac{dt}{dy} [/itex]
  7. Jun 23, 2012 #6
    Yep, perfect! :approve:
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