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Question: Answered & Verified by Expert
If A is a 3×3 non-singular matrix such that AA'=A'A and B=A-1A', then BB' equals, where X' denotes the transpose of the matrix X.
MathematicsMatricesJEE MainJEE Main 2014 (06 Apr)
Options:
  • A B-1
  • B B-1'
  • C I+B
  • D I
Solution:
2502 Upvotes Verified Answer
The correct answer is: I

A'=AT

AA'=A'A

B=A-1A'

B'=A-1A''=A''·A-1'=AA-1'

BB'=A-1A'·AA-1'

       =A-1·A·A'·A-1'     ∵  AA'=A'A

       =I·A'·A-1'

       =I·A-1A'           ∵  CD'=D'C'

       =I·I'

       =I2                                      ∵  I=I'

       =I

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