JEE Main 2014 (Offline)Question 1
If $A$ is a $3\times3$ non-singular matrix such that $AA'=A'A$ and $B=A^{-1}A'$, then $BB'$ equals :
Matrices
Solution
$B'=A(A')^{-1}$, so $BB'=A^{-1}A'A(A')^{-1}=A^{-1}AA'(A')^{-1}=I$ using $A'A=AA'$.Matrices - JEE Mathematics question (JEE Main 2014 (Offline))
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