JEE Main & Advanced Sample Paper JEE Main Sample Paper-42

  • question_answer
    The number of real solutions of\[{{\tan }^{-1}}\sqrt{x(x+1)}+{{\sin }^{-1}}\sqrt{{{x}^{2}}+x+1}=\frac{\pi }{2}\]

    A)  0                                

    B)  1

    C)  2                                

    D)  \[\infty \]

    Correct Answer: C

    Solution :

    From given function  \[{{\tan }^{-1}}\sqrt{x(x+1)}+{{\sin }^{-1}}\sqrt{{{x}^{2}}+x+1}=\frac{\pi }{2},\]it is clear that (1)\[x(x+1)\ge 0\] (\[\because \]Domain of square root function) (2) \[{{x}^{2}}+x+1\ge 0\](\[\because \]Domain of square root function) (3)\[{{x}^{2}}+x+1\le 1\]  (\[\because \] Domain of \[{{\sin }^{-1}}\] function) From (1), (2) and (3), \[(0\le {{x}^{2}}+x+1\le 1)\cap ({{x}^{2}}+x\ge 0)\] \[\Rightarrow \]\[(0\le {{x}^{2}}+x+1\le 1)\cap ({{x}^{2}}+x\ge 1)\] \[\Rightarrow \]\[{{x}^{2}}+x+1=1\]\[\Rightarrow \]\[{{x}^{2}}+x=0\]\[\Rightarrow \]\[x=0,x=-1\]


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