Engineering
Mathematics
Multiplication of Matrices
Symmetric and Skew Symmetric Matrices
Question

If A and B are symmetric matrices, then write the condition for which AB is also symmetric.

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Solution
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Given, A and B are symmetric matrices.

Then AT = A, BT = B      .......(1)
Now,
(AB)T
= BTAT
= BA [ Using (1)]             ......(2).
Now will be symmetric if (AB)T= AB i.e. we should have BA = AB.
This is the required condition. [ Using (2)]
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