Math Problem Statement

Q−1: Answer each of the following as True or False justifying your answers:

[3 marks] If A and B are symmetric matrices then ABA is skew-symmetric.

Solution

To determine whether the statement "If AA and BB are symmetric matrices, then ABAABA is skew-symmetric" is true or false, we need to analyze the properties of symmetric and skew-symmetric matrices.

Definitions

  1. Symmetric Matrix: A matrix AA is symmetric if AT=AA^T = A.
  2. Skew-Symmetric Matrix: A matrix CC is skew-symmetric if CT=CC^T = -C.

Given

  • AA and BB are symmetric matrices, i.e., AT=AA^T = A and BT=BB^T = B.

To Prove

We need to prove whether (ABA)T=ABA(ABA)^T = -ABA.

Proof

Let's find the transpose of ABAABA: (ABA)T=ATBTAT(ABA)^T = A^T B^T A^T

Since AA and BB are symmetric: AT=AandBT=BA^T = A \quad \text{and} \quad B^T = B

Substituting these into the equation, we get: (ABA)T=ABA(ABA)^T = A B A

Therefore: (ABA)T=ABA(ABA)^T = ABA

This implies that ABAABA is symmetric, not skew-symmetric.

Conclusion

Since (ABA)T=ABA(ABA)^T = ABA, which is not equal to ABA-ABA, the matrix ABAABA is not skew-symmetric.

Therefore, the statement is False.

The assertion that ABAABA is skew-symmetric when AA and BB are symmetric matrices is incorrect. Instead, ABAABA remains symmetric.

If you have further questions or need more details, feel free to ask!

Here are 8 related questions you might find interesting:

  1. What is the result when a symmetric matrix is multiplied by a skew-symmetric matrix?
  2. Can a matrix be both symmetric and skew-symmetric? If yes, what does that imply?
  3. How do the eigenvalues of a symmetric matrix differ from those of a skew-symmetric matrix?
  4. What is an example of a 2x2 skew-symmetric matrix?
  5. How can you determine if a matrix is symmetric by inspecting its entries?
  6. What are the properties of the transpose operation when applied to the product of matrices?
  7. Can a non-square matrix be symmetric?
  8. How does the determinant of a symmetric matrix relate to its eigenvalues?

Tip: When dealing with matrix transposes, remember that the transpose of a product of matrices reverses the order: (AB)T=BTAT(AB)^T = B^T A^T.

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Math Problem Analysis

Mathematical Concepts

Matrix Algebra
Symmetric Matrices
Skew-Symmetric Matrices
Matrix Transposition

Formulas

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Theorems

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Suitable Grade Level

Advanced Undergraduate