JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Morning)

  • question_answer
    lf\[\int_{{}}^{{}}{\frac{\sqrt{1-{{x}^{2}}}}{{{x}^{4}}}}dx=A(x){{(\sqrt{1-{{x}^{2}}})}^{m}}+C,\]for a suitable chosen integer m and a function A(x), where C is a constant of integration, then \[{{(A(x))}^{m}}\]equals [JEE Main Online Paper (Held On 11-Jan-2019 Morning]

    A) \[\frac{1}{9{{x}^{4}}}\]                                             

    B)               \[\frac{-1}{3{{x}^{3}}}\]

    C)               \[\frac{1}{27{{x}^{6}}}\]                               

    D)               \[\frac{-1}{27{{x}^{9}}}\]

    Correct Answer: D

    Solution :

    Let\[I=\int_{{}}^{{}}{\frac{\sqrt{1-{{x}^{2}}}}{{{x}^{4}}}}dx=\int_{{}}^{{}}{\frac{\sqrt[x]{\frac{1}{{{x}^{2}}}-1}}{{{x}^{4}}}}dx\] Put\[\frac{1}{{{x}^{2}}}-1=t\Rightarrow \frac{-2}{{{x}^{3}}}dx=dt\Rightarrow \frac{dx}{{{x}^{3}}}=-\frac{1}{2}dt\] \[\therefore \]\[I=-\frac{1}{2}\int_{{}}^{{}}{\sqrt{t}}dt=-\frac{1}{3}({{t}^{3/2}})+c\] \[=-\frac{1}{3}{{\left( \frac{1}{{{x}^{2}}}-1 \right)}^{3/2}}+c=-\frac{1}{3{{x}^{3}}}{{\left( 1-{{x}^{2}} \right)}^{3/2}}+c\] \[={{\frac{\left( \sqrt{1-{{x}^{2}}} \right)}{-3{{x}^{3}}}}^{3}}+c\] \[\therefore \]\[A(x)=-\frac{1}{3{{x}^{3}}}\]and\[m=3\] \[\therefore \]\[{{(A(x))}^{3}}={{\left( \frac{-1}{3{{x}^{3}}} \right)}^{3}}=-\frac{1}{27{{x}^{9}}}\]


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