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Let A be 3 x 3 matrix with real entries such that det(A) = 6 and the trace of A is 0. lf det(A + I) = 0 where I denotes the 3 x 3 identity matrix, then the eigenvalues of A are
  • a)
    -1, 2, 3
  • b)
    -1, 2, -3
  • c)
    1, 2, -3
  • d)
    -1, -2, 3
Correct answer is option 'D'. Can you explain this answer?
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Let A be 3 x 3 matrix with real entries such that det(A) = 6 and the t...
Given Information:
- A is a 3x3 matrix with real entries.
- det(A) = 6
- The trace of A is 0.
- det(A + I) = 0, where I denotes the 3x3 identity matrix.

To Find:
The eigenvalues of matrix A.

Solution:

1. Trace of a Matrix:
The trace of a square matrix is the sum of its diagonal elements. Given that the trace of matrix A is 0, we have:
Trace(A) = 0

2. Eigenvalues and Determinant:
The determinant of a matrix is equal to the product of its eigenvalues. We are given that det(A) = 6. Since the matrix A is 3x3, it has three eigenvalues (possibly repeated).

3. Determinant of (A + I):
We are given that det(A + I) = 0. The determinant of a matrix is also equal to the product of its eigenvalues. So, the product of the eigenvalues of (A + I) is 0.

4. Product of Eigenvalues:
Let the eigenvalues of A be λ1, λ2, and λ3. The eigenvalues of (A + I) will be (λ1 + 1), (λ2 + 1), and (λ3 + 1). Since the product of the eigenvalues of (A + I) is 0, we have:
(λ1 + 1) * (λ2 + 1) * (λ3 + 1) = 0

5. Eigenvalues of A:
Since the product of the eigenvalues of (A + I) is 0, at least one of the eigenvalues of (A + I) must be 0. This means at least one of the eigenvalues of A must be -1.

6. Eigenvalues of A:
The determinant of A is equal to the product of its eigenvalues. We are given that det(A) = 6. Since one eigenvalue is -1, the product of the other two eigenvalues must be -6.

7. Possible Eigenvalues of A:
Considering the product of the other two eigenvalues of A is -6, and the eigenvalues are real, the possible eigenvalues are:
-1, -2, 3
-1, 2, -3
1, -2, 3
1, 2, -3

8. Eigenvalues of A:
Since the trace of A is 0, the sum of its eigenvalues is 0. Among the possible eigenvalues, only the set -1, -2, 3 satisfies this condition.

Final Answer:
Therefore, the eigenvalues of matrix A are -1, -2, and 3, which matches option 'D'.
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Let A be 3 x 3 matrix with real entries such that det(A) = 6 and the t...
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Let A be 3 x 3 matrix with real entries such that det(A) = 6 and the trace of A is 0. lf det(A + I) = 0 where I denotes the 3 x 3 identity matrix, then the eigenvalues of A area)-1, 2, 3b)-1, 2, -3c)1, 2, -3d)-1, -2, 3Correct answer is option 'D'. Can you explain this answer?
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