Complex Eigenvalues of system of DE

Click For Summary
The discussion centers on clarifying the equivalence between two expressions in the context of complex eigenvalues in a system of differential equations. A participant expresses confusion regarding a transition between steps, specifically pointing out a sign error in the yellow expression. The correct form of the second term is identified as involving a negative sine and a positive cosine. Acknowledgment of a typo resolves the confusion, leading to a clearer understanding of the mathematical relationship. The conversation highlights the importance of accuracy in mathematical expressions when dealing with complex systems.
member 731016
Homework Statement
Please see below.
Relevant Equations
Please see below
For this problem,
1715292619315.png

1715292474940.png

Can someone please explain to me how they got from the orange step to the yellow step?

I am confused how the two expressions are equivalent.

Thanks!
 

Attachments

  • 1715292574625.png
    1715292574625.png
    17.4 KB · Views: 58
Physics news on Phys.org
Just perform the multiplications and collect real and imaginary terms in their own matrices.
 
  • Like
  • Love
Likes member 731016 and FactChecker
ChiralSuperfields said:
I am confused how the two expressions are equivalent.
The yellow expression contains a sign error; the second term should be:$$
i\left(\begin{array}{c}
-e^{-2t}\sin3t\\
+e^{-2t}\cos3t
\end{array}\right)
$$
 
  • Love
Likes member 731016
Thank you for your replies @Orodruin and @renormalize ! Yeah that was part of my confusion is that there is a typo
1715294433735.png

It makes sense now that I know it is a typo!

Thanks!
 
First, I tried to show that ##f_n## converges uniformly on ##[0,2\pi]##, which is true since ##f_n \rightarrow 0## for ##n \rightarrow \infty## and ##\sigma_n=\mathrm{sup}\left| \frac{\sin\left(\frac{n^2}{n+\frac 15}x\right)}{n^{x^2-3x+3}} \right| \leq \frac{1}{|n^{x^2-3x+3}|} \leq \frac{1}{n^{\frac 34}}\rightarrow 0##. I can't use neither Leibnitz's test nor Abel's test. For Dirichlet's test I would need to show, that ##\sin\left(\frac{n^2}{n+\frac 15}x \right)## has partialy bounded sums...