JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Determinats

  • question_answer
    The determinant \[\left| \begin{matrix}    x & \sin \theta  & \cos \theta   \\    -\sin \theta  & -x & 1  \\    \cos \theta  & 1 & x  \\ \end{matrix} \right|\] is independent of

    A) x only

    B) \[\theta \] only

    C) x and \[\theta \] both

    D) None of these

    Correct Answer: B

    Solution :

    [b]  \[\left| \begin{matrix}    x & \sin \theta  & \cos \theta   \\    -\sin \theta  & -x & 1  \\    \cos \theta  & 1 & x  \\ \end{matrix} \right|\] \[=x({{x}^{2}}-1)-\sin \theta (-x\sin \theta -\cos \theta )\]                         \[+\cos \theta (-\sin \theta +x\cos \theta )\] \[=-{{x}^{3}}-x+x{{\sin }^{2}}\theta +\sin \theta \cos \theta \]             \[-\cos \theta \sin \theta +x{{\cos }^{2}}\theta )\] \[={{x}^{3}}-x+x={{x}^{3}}\]


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