JEE Main & Advanced Sample Paper JEE Main Sample Paper-14

  • question_answer
    Let A be a \[n\times n\] matrix such that \[{{a}_{ij}}={{\sin }^{-1}}\,(\sin \,(i-j))\,\forall \,i\] and j. Which of the following is true?

    A)  If n is odd, then A is an invertible matrix,     

    B)  If n is even, then A is not an invertible matrix,

    C)  For all values of n, A is not invertible matrix,

    D)  A is a skew-symmetric matrix.

    Correct Answer: D

    Solution :

     Let \[A=\left[ \begin{matrix}    0 & {{\sin }^{-1}}(-1) & {{\sin }^{-1}}(-2)  \\    {{\sin }^{-1}}(1) & 0 & {{\sin }^{-1}}(-1)  \\    {{\sin }^{-1}}(2) & {{\sin }^{-1}}(1) & 0  \\ \end{matrix} \right]\] \[=\left[ \begin{matrix}    0 & -{{\sin }^{-1}}(-1) & -{{\sin }^{-1}}(-2)  \\    {{\sin }^{-1}}(1) & 0 & -{{\sin }^{-1}}(-1)  \\    {{\sin }^{-1}}(2) & {{\sin }^{-1}}(1) & 0  \\ \end{matrix} \right]\] As the matrix is skew-symmetric hence, \[|A|\,=0,\] if n is odd. \[\Rightarrow \] A is not an invertible matrix, when n is odd.


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