JEE Main & Advanced Sample Paper JEE Main - Mock Test - 39

  • question_answer
    If \[y={{e}^{{{\sin }^{-1}}x}}+{{e}^{-{{\cos }^{-1}}x}},\] then the value of \[\left| \frac{y''({{x}^{2}}-1)+y}{xy'} \right|\]is (where \[y'\]and \[y''\]denote first order and second order derivatives of y, respectively)

    A) \[1\]                     

    B)        \[0\]                       

    C) \[1/2\]                   

    D)        \[2\]

    Correct Answer: A

    Solution :

    [a] \[y={{e}^{{{\sin }^{-1}}x}}+{{e}^{-{{\cos }^{-1}}x}}={{e}^{{{\sin }^{-1}}x}}+{{e}^{\frac{\pi }{2}+{{\sin }^{-1}}x}}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,y={{e}^{{{\sin }^{-1}}x}}(1+{{e}^{-\pi /2}})\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,y'=\frac{{{e}^{{{\sin }^{-1}}x}}}{\sqrt{1-{{x}^{2}}}}\,\,(1+{{e}^{-\pi /2}})\Rightarrow y'=\frac{y}{\sqrt{1-{{x}^{2}}}}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,(1-{{x}^{2}})\,{{(y')}^{2}}={{y}^{2}}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,2y'y''(1-{{x}^{2}})+{{(y')}^{2}}(-2x)=2yy'\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,y''(1-{{x}^{2}})+y'(-x)=y\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\left| \frac{({{x}^{2}}-1)\,y''+y}{y'x} \right|=1\]


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