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The product of all eigenvalues of the matrix | 1 2 3 | | 4 5 6 | | 7 8 9 | is A. -1 B. 0 C. 1 D. 2

GATE 2024 · Engineering Mathematics · Eigen Value · medium

Answer: Product of all eigenvalues = det(M) = 0. Answer: B

  1. Check row linear dependence: R2 - R1 = [4-1, 5-2, 6-3] = [3, 3, 3] R3 - R2 = [7-4, 8-5, 9-6] = [3, 3, 3] Since R3 - R2 = R2 - R1, we have R3 = 2*R2 - R1. The rows are linearly dependent.
  2. Conclude determinant equals zero: Since rows are linearly dependent, det(M) = 0. Therefore product of eigenvalues = det(M) = 0.