KVPY Sample Paper KVPY Stream-SX Model Paper-28

  • question_answer
    \[{{\sin }^{-1}}(\sin 5)>{{x}^{2}}-4x\]holds if

    A) \[x<2-\sqrt{9-2\pi }\]

    B) \[-1<x<5\]

    C) \[x\in \left( -\infty ,-1 \right)\cup \left( 5,\infty  \right)\]

    D) \[x\in \left( 2-\sqrt{9-2\pi },2+\sqrt{9-2\pi } \right)\]

    Correct Answer: D

    Solution :

    \[\therefore \]\[\frac{3\pi }{2}<5<\frac{5\pi }{2}\therefore {{\sin }^{-1}}\left( \sin 5 \right)=5-2\pi \]
    Given \[{{\sin }^{-1}}\left( \sin 5 \right)>{{x}^{2}}-4x\Rightarrow {{x}^{2}}-4x<5-2\pi \] \[\Rightarrow \]\[{{x}^{2}}-4x+\left( 2\pi -5 \right)<0\]
    Roots of \[{{x}^{2}}-4x+2\pi -5=0\]are \[2\pm \sqrt{9-2\pi }\]
    \[\therefore \]\[{{x}^{2}}-4x+2\pi -5<0\] \[\Rightarrow \]\[2-\sqrt{9-2\pi }<x<2+\sqrt{9-2x}\]


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