Show how to classify a quadratic form Q(x) = x T Ax, when and det A

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Show how to classify a quadratic form Q(x) = xTAx, when image and det A ≠ 0, without finding the eigenvalues of A.


If λ1 and λare the eigenvalues of A, then the characteristic of A can be written in two ways: det(A - λI) and (λ – λ) (λ – λ2) Use this fact to show that λ+ λ2 = a + d (the diagonal entries of A) and λ1λ= det A.

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Linear Algebra And Its Applications

ISBN: 9781292351216

6th Global Edition

Authors: David Lay, Steven Lay, Judi McDonald

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