KVPY Sample Paper KVPY Stream-SX Model Paper-27

  • question_answer
    If \[\alpha \] is a real root of the equation \[{{x}^{2}}+3x-\tan \left( \frac{1}{2} \right)=0,\] then \[{{\cot }^{-1}}\alpha +{{\cot }^{-1}}\frac{1}{\alpha }-\frac{\pi }{2}\] is equal to-

    A) 0

    B) \[\frac{\pi }{2}\]   

    C) \[\pi \]

    D) \[\frac{3\pi }{2}\]

    Correct Answer: C

    Solution :

    \[D>0;\] \[\alpha +\beta <0\Rightarrow \alpha <0;\] \[\beta <0\]
    \[\therefore {{\cot }^{-1}}\alpha +{{\cot }^{-1}}\left( \frac{1}{\alpha } \right)-\frac{\pi }{2}\]
    \[={{\cot }^{-1}}\alpha +\pi +{{\tan }^{-1}}\alpha -\frac{\pi }{2}\]
    \[=\pi +\frac{\pi }{2}-\frac{\pi }{2}=\pi \]


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