When finding the frequencies of normal modes, can you have a negative frequency?

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Do you simply just consider the positive solutions? I tried a google search but didn't find anything quickly. The work I am studying is Lagrangian systems.

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No you cannot have negative frequencies. I assume you are studying lagrangian mechanics and using $$ \det(V-\omega^2 T)=0 $$ in order to calculate frequencies, where V and T are potential and kinetic energy matrices. We can have an angular frequency $\omega=0$, or $\omega >0$, but never $\omega <0$. Any more questions let me know.

So to answer your question, you take only the positive root when calculating $\omega$.