Which of the following are correct?
(A) If A and B are symmetric matrices such that AB = BA, then AB is symmetric.
(B) If A and B are symmetric matrices of the same order, then (A+B) is a symmetric matrix.
(C) If A and B are symmetric matrices of the same order, then (AB-BA) is a symmetric matix.
(D) If A and B are symmetric matrices of the same order, then (AB+BA) is a skew symmetric matrix
Choose the correct answer from the options given below:
Which of the following are correct?
(A) If A and B are symmetric matrices such that AB = BA, then AB is symmetric.
(B) If A and B are symmetric matrices of the same order, then (A+B) is a symmetric matrix.
(C) If A and B are symmetric matrices of the same order, then (AB-BA) is a symmetric matix.
(D) If A and B are symmetric matrices of the same order, then (AB+BA) is a skew symmetric matrix
Choose the correct answer from the options given below:
Solution
A matrix is symmetric if it equals its own transpose:
For symmetric matrices A and B: and
Transpose rule:
Statement (A): If AB = BA and both are symmetric, then AB is symmetric.
(given that AB = BA)
Therefore , so AB is symmetric.
Statement (A) is correct.
Statement (B): (A+B) is symmetric.
Therefore , so (A+B) is symmetric.
Statement (B) is correct.
Statement (C): (AB-BA) is symmetric.
Therefore , so (AB-BA) is skew-symmetric, not symmetric.
Statement (C) is incorrect.
Statement (D): (AB+BA) is skew-symmetric.
Therefore , so (AB+BA) is symmetric, not skew-symmetric.
Statement (D) is incorrect.
Only statements (A) and (B) are correct.
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