Similar Eigenvalues of Invertible Matrices

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In summary, the problem asks to prove that two matrices, A and C^-1AC, have the same eigenvalues when C is an invertible nxn matrix. The attempt at a solution involves using the determinant of matrices and factoring out CC^-1, but it is incorrect to assume that C^-1AC=C^-1CA. Further consideration is needed to solve the problem.
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muzziMsyed21
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Homework Statement



Let A and C be nxn matrices with C invertible. Prove that A and C-1AC have the same eigenvalues.


Homework Equations



B=C-1AC

The Attempt at a Solution



det(A-λI) =det(B-λI)
det(A-λI) =det(C-1AC - λI)
det(A-λI) =det(C-1AC - λC-1IC)
det(A-λI) =det[CC-1(A-λI)] <<<< can you factor out a CC-1??
 
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  • #2
muzziMsyed21 said:

Homework Statement



Let A and C be nxn matrices with C invertible. Prove that A and C-1AC have the same eigenvalues.


Homework Equations



B=C-1AC

The Attempt at a Solution



det(A-λI) =det(B-λI)
det(A-λI) =det(C-1AC - λI)
det(A-λI) =det(C-1AC - λC-1IC)
det(A-λI) =det[CC-1(A-λI)] <<<< can you factor out a CC-1??

You can't say C^(-1)AC=C^(-1)CA. The matrices A and C might not commute. Back up a step and think about it again.
 

1. What does it mean for eigenvalues to be similar?

Eigenvalues are considered similar if they have the same value or are equal to a constant multiple of each other. In other words, the only difference between similar eigenvalues is a scaling factor.

2. How do you prove that two eigenvalues are similar?

To prove that two eigenvalues are similar, you need to show that they are equal or that one is a constant multiple of the other. This can be done by solving the characteristic equation for both eigenvalues and comparing the results.

3. What is the significance of proving similar eigenvalues?

Proving similar eigenvalues is important in linear algebra because it allows us to simplify calculations and understand the relationship between different matrices. It also helps us identify patterns and similarities between different systems.

4. Can two matrices have similar eigenvalues but different eigenvectors?

Yes, it is possible for two matrices to have similar eigenvalues but different eigenvectors. This is because the eigenvectors are not unique and can be scaled or multiplied by a constant without changing the corresponding eigenvalue.

5. Are similar eigenvalues always associated with similar matrices?

No, similar eigenvalues do not always mean that the matrices are similar. Two matrices are considered similar if they have the same eigenvalues and corresponding eigenvectors. However, two matrices can have similar eigenvalues but different eigenvectors, which means they are not similar.

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