Question:

If \( A \) is an \( n \times n \) non-singular matrix such that \( AA^T = A^{-1}A \) and \( B = A^{-1}A^T \), then \( BB' \) is equal to

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Transpose reverses order — very important in matrix simplifications!
Updated On: Apr 22, 2026
  • \( I + B \)
  • \( I \)
  • \( B^{-1} \)
  • \( (B^{-1})' \)
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The Correct Option is B

Solution and Explanation

Concept: Use properties: \[ (A^T)^T = A,\quad (AB)^T = B^TA^T \]

Step 1:
Given.
\[ B = A^{-1}A^T \]

Step 2:
Transpose.
\[ B' = (A^{-1}A^T)^T = A(A^{-1})^T \]

Step 3:
Multiply.
\[ BB' = A^{-1}A^T \cdot A(A^{-1})^T = I \]
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