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Question
If A and B are two non singular matrices and both are symmetric and commute each other then
Options:
A .  Both A−1B and A−1B−1 are symmetric
B .  A−1B is symmetric but A−1B−1 is not symmetric
C .  A−1B−1  is symmetric but A−1B is not symmetric
D .  Neither A−1B nor A−1B−1 are symmetric
Answer: Option A
:
A
AB =BA
Previous & past multiplying both sides by A1.
A1(AB)A1=A1(BA)A1(A1A)(BA1)=A1B(AA1)(BA1)1=(A1B)1=(A1)1B1(reversallaws)=A1B(asB=B1)(A1)1=A1A1B is symmetric
Similarly for A1B1.

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