12th Class Mathematics Determinants Question Bank Assertion And Reason (MCQs) - Determinants

  • question_answer
    Assertion : \[\left| AA' \right|=0\]
    Reason: A is skew matrix.

    A) Both A and R are individually true and R is the correct explanation of A.

    B) Both A and R are individually true and R is not the correct explanation of A.

    C) 'A' is true but 'R' is false

    D) 'A' is false but 'R' is true

    E) Both A and R are false.

    Correct Answer: C

    Solution :

    Given Assertion is \[\left| AA' \right|=0\Rightarrow \left| A \right|\,\,\left| A' \right|=0\] ...(1)
    \[\Rightarrow \]either \[\left| A \right|\text{ }=\text{ }0\] or \[\left| A' \right|\text{ }=\text{ }0\]
    Or
    \[\left| A \right|=0\] and \[\left| A' \right|=0\]
    We know that \[\left| A \right|=\left| A' \right|\]
    \[\therefore \]from (1) \[\left| A \right|\,\,\,\left| A \right|=0\Rightarrow \,{{\left| A \right|}^{2}}=0\,\,\Rightarrow \left| A \right|=0\]
    .'. Assertion is\[\left| A \right|=0\].
    Also Reason is A is skew symmetric matrix.
    We know that \[\left| A \right|=0\], when order of skew matrix A is odd and \[\left| A \right|\ne 0\], when order of skew matrix is even
    \[\therefore \]Assertion \[\left| A \right|=0\] is not valid for shew symmetric matrix of even order
    \[\therefore \]Reasion : A is skew symmetric is not valid reason for Assertion : \[\left| AA' \right|=0\].
    A is true but R is false
    Hence option [C] is the correct answer.


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