Directions : In the following questions, A statement of Assertion (A) ...
Generally (AB)’ = B’ A’
If AB = BA, then (AB)’ = (BA)’ = A’ B’ = AB
Since (AB)’ = AB, AB is a symmetric matrix. Hence R is true.
A(BA) = (AB)A = ABA
(ABA)’ = A’ B’ A’ = ABA.
A(BA) and (AB)A are symmetric matrices. Hence A is true.
But R is not the correct explanation for A.
Directions : In the following questions, A statement of Assertion (A) ...
Assertion (A): A(BA) and (AB)A are symmetric matrices.
Reason (R): AB is a symmetric matrix if the matrix multiplication of A with B is commutative.
Explanation:
To prove this assertion, we need to show that both statements A and R are true and that statement R is the correct explanation of statement A.
Statement A: A(BA) and (AB)A are symmetric matrices.
Let's consider the matrix A and B to be symmetric matrices of order 3.
A matrix is said to be symmetric if it is equal to its transpose. In other words, for a matrix A, A = A^T.
Now, let's analyze the matrix products A(BA) and (AB)A.
Matrix Product A(BA):
A(BA) = A(BA)^T [Since A(BA) is symmetric, it is equal to its transpose]
= A(AB)^T [Since (BA)^T = (AB)^T]
= (A^T)(AB) [Using the property of transpose]
= (AB)A [Since A^T = A]
Therefore, A(BA) is a symmetric matrix.
Matrix Product (AB)A:
(AB)A = (AB)A^T [Since (AB)A is symmetric, it is equal to its transpose]
= AB^TA^T [Using the property of transpose]
= AB^TA [Since A^T = A]
Therefore, (AB)A is a symmetric matrix.
Statement R: AB is a symmetric matrix if the matrix multiplication of A with B is commutative.
A matrix product AB is commutative if AB = BA, i.e., the order of multiplication does not matter.
If AB is commutative, then (AB)A = A(BA) = A^T(BA) = (BA)A = BA^TA = BA.
Thus, if AB is commutative, then both A(BA) and (AB)A are symmetric matrices.
Conclusion:
From the above analysis, we can conclude that both statement A and statement R are true. Furthermore, statement R is the correct explanation of statement A, as the commutativity of matrix multiplication (AB = BA) ensures that both A(BA) and (AB)A are symmetric matrices. Hence, the correct answer is option 'B'.