JEE Main & Advanced Sample Paper JEE Main - Mock Test - 17

  • question_answer
    Let \[A=[{{a}_{ij}}]\]be a \[3\times 3\] invertible matrix. If determinant value of matrix A is 3, then the value of det. \[({{(adj\,.{{A}^{T}})}^{T}})+\det .({{(adj.{{A}^{-1}})}^{-1}})\]is

    A) 3                      

    B)        9       

    C) 12                     

    D)        18

    Correct Answer: B

    Solution :

    [b] \[\det ({{(adj{{A}^{T}})}^{T}})=\det \,(adj\,{{A}^{T}})\] \[={{(\det ({{A}^{T}}))}^{2}}={{(\det \,A)}^{2}}=9\] \[\det \,({{(adj{{A}^{-1}})}^{-1}})=\frac{1}{\det \,\left( adj\,{{A}^{-1}} \right)}\] \[=\frac{1}{{{\left( \det \left( {{A}^{-1}} \right) \right)}^{2}}}={{\left( \det A \right)}^{2}}=9\]             


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