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Suppose A and B are symmetric and AB = BA. Prove there is an orthogonal matrix Q so that
Chapter 6, Problem 15(choose chapter or problem)
Suppose A and B are symmetric and AB = BA. Prove there is an orthogonal matrix Q so that both Q 1AQ and Q 1BQ are diagonal. (Hint: Let be an eigenvalue of A. Use the Spectral Theorem to show that there is an orthonormal basis for E() consisting of eigenvectors of B.)
Questions & Answers
QUESTION:
Suppose A and B are symmetric and AB = BA. Prove there is an orthogonal matrix Q so that both Q 1AQ and Q 1BQ are diagonal. (Hint: Let be an eigenvalue of A. Use the Spectral Theorem to show that there is an orthonormal basis for E() consisting of eigenvectors of B.)
ANSWER:Step 1 of 2
Given that and are symmetric matrices with .
To prove there is an orthogonal matrix such that both and are diagonal.
Since is symmetric, by spectral theorem, eigenvalues of are real and there is an orthonormal basis of consisting of eigenvectors of .
Now, suppose be an eigenvector of corresponding to an arbitrary eigenvalue . Then, by definition,
.