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

  • question_answer
    If \[y=\left| \begin{matrix}    \sin x & \cos x & \sin x  \\    \cos x & -\operatorname{sinx} & \cos x  \\    x & 1 & 1  \\ \end{matrix} \right|,\]then \[\frac{dy}{dx}\] is

    A) \[1\]

    B) \[2\]

    C) \[3\]

    D) 0

    Correct Answer: A

    Solution :

    [a] \[\frac{dy}{dx}=\left| \begin{matrix}    \cos x & -\sin x & \cos x  \\    \cos x & -\sin x & \cos x  \\    x & - & -  \\ \end{matrix} \right|\] \[+\left| \begin{matrix}    \sin x & \cos x & sinx  \\    -\sin x & -\cos x & -\sin x  \\    x & 1 & 1  \\ \end{matrix} \right|\] \[+\left| \begin{matrix}    \sin x & \cos x & sinx  \\    \cos x & -sinx & \cos x  \\    x & 0 & 0  \\ \end{matrix} \right|\] \[=0-\left| \begin{matrix}    \sin x & \cos x & sinx  \\    sinx & \cos x & sinx  \\    x & 1 & 1  \\ \end{matrix} \right|\]\[+1\left| \begin{matrix}    \cos x & \sin x  \\    -\sin x & \cos x  \\ \end{matrix} \right|\] \[=0+({{\cos }^{2}}x+{{\sin }^{2}}x)\]


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