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Weird ODE containing cos.by Reid
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#1
Nov1108, 10:31 AM

P: 36

1. The problem statement, all variables and given/known data
I can not determine the solution to the diff. eq. 2. Relevant equations [tex]\ddot{x}+k \cos{x}=0[/tex]. The constant k is postive. 3. The attempt at a solution I tried solving it with the methods I know and it all ended up in a big mess. I am just not used to the second term, \cos. Doe's anyone know what to do? 


#2
Nov1108, 10:37 AM

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Sci Advisor
PF Gold
P: 4,500

It's GOT to be something of the form
[tex]x=arccos(y)[/tex] for some y a function of t, based on an argument of 'this is really fricking hard otherwise'. Try the substitution and see what you get 


#3
Nov1108, 12:51 PM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,553

I am not sure that is going to be easy to integrate, but that gives the solution. 


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