JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Types of matrices, Algebra of matrices

  • question_answer
     If \[A+B=\left[ \begin{matrix}    1 & 0  \\    1 & 1  \\ \end{matrix} \right]\]and \[A-2B=\left[ \begin{matrix}    -1 & 1  \\    0 & -1  \\ \end{matrix} \right]\,,\]then A= [Karnataka CET 1994]

    A) \[\left[ \begin{matrix}    1 & 1  \\    2 & 1  \\ \end{matrix} \right]\]

    B) \[\left[ \begin{matrix}    2/3 & 1/3  \\    1/3 & 2/3  \\ \end{matrix} \right]\]

    C) \[\left[ \begin{matrix}    1/3 & 1/3  \\    2/3 & 1/3  \\ \end{matrix} \right]\]

    D) None of these

    Correct Answer: C

    Solution :

      \[2A+2B=\left[ \begin{matrix}    2 & 0  \\    2 & 2  \\ \end{matrix} \right]\], \[A-2B=\left[ \begin{matrix}    -1 & 1  \\    0 & -1  \\ \end{matrix} \right]\] On adding, we get\[3A=\left[ \begin{matrix}    1 & 1  \\    2 & 1  \\ \end{matrix} \right]\] \[\Rightarrow \,A=\left[ \begin{matrix}    1/3 & 1/3  \\    2/3 & 1/3  \\ \end{matrix} \right]\].


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