JEE Main & Advanced Sample Paper JEE Main - Mock Test - 35

  • question_answer
    If \[\frac{d}{dx}(x)=f'(x),\] then \[\int{\frac{xf'(x)-2f(x)}{\sqrt{{{x}^{4}}f(x)}}}\,dx\] is equal  to

    A) \[{{x}^{2}}f(x)+c\]     

    B)        \[|x|\,f(x)+c\]

    C) \[|x|\sqrt{f(x)}+c\]       

    D)        \[\frac{2\sqrt{f(x)}}{|x|}+c\]

    Correct Answer: D

    Solution :

    [d] \[I=\int{\frac{xf'(x)-2f(x)}{{{x}^{2}}\sqrt{f(x)}}}\,\,dx=\int{\frac{\frac{{{x}^{2}}f'(x)-2x(x)}{{{x}^{4}}}}{\sqrt{\frac{f(x)}{{{x}^{2}}}}}}dx\] Let \[\frac{f(x)}{{{x}^{2}}}=t.\] \[\Rightarrow \,\,\,I=\int{\frac{dt}{\sqrt{t}}}=2\sqrt{t}+c\] \[=2\sqrt{\frac{f(x)}{{{x}^{2}}}}+c\] \[=\frac{2\sqrt{f(x)}}{|x|}+c\]


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