Let A be an n×n real symmetric matrix. Prove that if λ is an eigenvalue of A of multiplicity n, thenA is a scalar matrix. [Hint: Prove that there exists an orthogonal matrix S such that ST AS=λIn, and then solve for A.]

Linear Algebra: A Modern Introduction
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Chapter4: Eigenvalues And Eigenvectors
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Let A be an n×n real symmetric matrix. Prove that if λ is an eigenvalue of A of multiplicity n, thenA is a scalar matrix. [Hint: Prove that there exists an orthogonal matrix S such that ST AS=λIn, and then solve for A.]

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Given that A is a n×n real symmetric matrix.

We have to prove that  if λ is an eigenvalue of A of multiplicity n, then A is a scalar matrix.

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