JEE Main & Advanced Sample Paper JEE Main Sample Paper-32

  • question_answer
    If \[{{\cos }^{-1}}x={{\sin }^{-1}}3x,\]then sum of all possible values of x equals

    A) 0                             

    B)    \[\frac{1}{\sqrt{10}}\]

    C) \[\frac{2}{\sqrt{10}}\]                   

    D)    \[\frac{-2}{\sqrt{10}}\]

    Correct Answer: B

    Solution :

    \[\alpha =\beta \] \[\therefore \,\,\sin \,\alpha \,=\sin \,\beta \] \[\Rightarrow \,\sqrt{1-{{x}^{2}}}=3x\] \[\Rightarrow \,1-{{x}^{2}}=9{{x}^{2}}\,\Rightarrow \,10{{x}^{2}}-1\] \[\Rightarrow \,x=\frac{1}{\sqrt{10}}\,\,,\,\frac{-1}{\sqrt{10}}\] \[\therefore \,\,x=\frac{1}{\sqrt{10}}\]


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