(adsbygoogle = window.adsbygoogle || []).push({}); 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?

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# Homework Help: Weird ODE containing cos.

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