3 and 4 .Determinants and Matrices
easy

यदि $A$ तथा $B$ समान कोटि के सममित आव्यूह हैं तो $AB - BA$ एक

A

शून्य अव्यूह है

B

सममित आव्यूह है

C

विषम सममित आव्यूह है

D

तत्समक आव्यूह है

Solution

$A$ and $B$ are symmetric matrices, therefore, we have :

$A^{\prime}=A$ and $B^{\prime}=B$  ………. $(1)$

Consider $(A B-B A)^{\prime} =(A B)^{\prime}-(B A)^{\prime}$   $[\because $   $=A^{\prime} -B^{\prime}] $

$=B^{\prime} A^{\prime}-A^{\prime} B^{\prime}$  $ [ \because $  $B^{\prime} A^{\prime}]$

$=B A-A B $   $[$  by $(1)$ $]$

$=-\,(A B-B A)$

$\therefore  $ $(A B-A B)^{\prime} =-(A B-B A)$

Thus, $(A B-B A)$ is a skew-symmetric matrix.

Standard 12
Mathematics

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