JEE Main & Advanced Sample Paper JEE Main Sample Paper-17

  • question_answer
    The values of\[\theta \]and\[\lambda \]in the following equations\[\sin \theta x-\cos \theta y+(\lambda +1)z=0;\] \[\cos \theta x+\sin \theta y-\lambda z=0;\] \[\lambda x+(\lambda +1)y+\cos \theta z=0\] have non trivial solution, are              

    A) \[\theta =n\pi ,\,\lambda \in R-\{0\}\]

    B)  \[\theta =2n\pi ,\lambda \]is any rational number

    C)  \[\theta =(2n+1)\pi ,\lambda \in {{R}^{+}},n\in I\]

    D)  \[\theta =(2n+1)\frac{\pi }{2},\lambda \in R,n\in I\]

    Correct Answer: D

    Solution :

     For non trivial solution \[\left| \begin{matrix}    sin\theta  & -\cos \theta  & \lambda +1  \\    \cos \theta  & \sin \theta  & -\lambda   \\    \lambda  & \lambda +1 & \cos \theta   \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[{{\sin }^{2}}\theta \cos \theta +{{\lambda }^{2}}\cos \theta +{{(\lambda +1)}^{2}}\cos \theta -\] \[\sin \theta \lambda (\lambda +1)+co{{s}^{3}}\theta +\sin \theta \lambda (\lambda +1)=0\] \[\Rightarrow \]\[2\cos \theta ({{\lambda }^{2}}+\lambda +1)=0\] \[\Rightarrow \]\[\cos \theta =0\] \[\Rightarrow \]\[\theta =(2n+1)\frac{\pi }{2},\lambda \in R,\,n\in I\]


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