Can Eigenfrequencies Explain Oscillatory Behavior in this Dynamical System?

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The discussion focuses on modeling a dynamical system using coupled ordinary differential equations, where oscillatory behavior can arise under certain conditions. The user is working to find the eigenfrequencies of the system by setting up a matrix from the equations and calculating its determinant. They propose that eigenfrequencies represent the oscillation frequencies of the system, with motion being a superposition of these modes. The user is exploring the relationship between the form of the solutions and the nature of damped oscillations, noting that imaginary eigenfrequencies indicate damping. This approach aims to demonstrate the existence of normal modes and their impact on the system's behavior.
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Homework Statement

Someone studying a dynamical system in another field of science tells you that when they
attempt to model the experiment they’ve been examining they obtain the following set of
coupled ordinary differential equations.

\dot{x}= -Ax + By
\dot{y}= -Cx

In what follows you should assume that the material parameters A, B, C are all positive and
non zero. They also tell you that for certain material parameters (that is, for certain A, B, C)
they can sometimes obtain oscillatory behaviour, albeit damped, but sometimes they do not.
Note that x and y are restricted to be real.

(a) Show that this is indeed possible by solving for the normal modes of this system. That is,
find the eigenfrequencies for this system.

The Attempt at a Solution



So basically my idea of eigenfrequencies are the frequencies at which the system oscillates and all motion of the system is the superposition of these two frequencies/motions. The first thing I'm doing is putting the constants into a matrix:

| -A B | |x| = |0|
| C 0 | |y|= |0|

Then i solve for determinant and get the eigenfrequencies. Basically I just wanted to know if I'm on the right track and this will help me prove that this is solving for the normal modes.
 
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Normal modes imply:

x(t) = D e^{i\omega t}

So you need to plug in similar functions for x and y. Then you solve for the eigenfrequences.
 
Shouldn't the function you plug in be of the form of a solution for a damped oscillation?
 
If \omega is imaginary then it will be damped.
 

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