JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Special types of matrices, Transpose, Adjoint and Inverse of matrices

  • question_answer
    If \[R(t)=\left[ \begin{matrix}    \cos t & \sin t  \\    -\sin t & \cos t  \\ \end{matrix} \right],\]then \[R(s).\,R(t)=\] [Roorkee 1981]

    A) \[R(s)+R(t)\]

    B) \[R\,(st)\]

    C) \[R(s+t)\]

    D) None of these

    Correct Answer: C

    Solution :

    \[R(s)\,R(t)=\left[ \begin{matrix}    \cos s & \sin s  \\    -\sin s & \cos s  \\ \end{matrix} \right]\,\left[ \begin{matrix}    \cos t & \sin t  \\    -\sin t & \cos t  \\ \end{matrix} \right]\]                   = \[\left[ \begin{matrix}    \cos (s+t) & \sin (t+s)  \\    -\sin (s+t) & \cos (t+s)  \\ \end{matrix} \right]=R(s+t)\].


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