JEE Main & Advanced Sample Paper JEE Main Sample Paper-23

  • question_answer
    The solution of the differential equation, \[xy\frac{dy}{dx}=\frac{1+{{y}^{2}}}{1+{{x}^{2}}}(1+x+{{x}^{2}})\] given that when \[x=1,y=0\] is

    A)  \[\ln \sqrt{1+{{y}^{2}}}=\ln (x)+{{\tan }^{-1}}(x)-\frac{\pi }{2}\]

    B)  \[\ln \left( \frac{1+{{y}^{2}}}{{{x}^{2}}} \right)=2{{\tan }^{-1}}(x)-\frac{\pi }{2}\]

    C)  \[\ln \left( \frac{1+{{y}^{2}}}{{{x}^{2}}} \right)=\frac{\pi }{4}-2{{\tan }^{-1}}x\]

    D)  \[\ln \left( \frac{1+{{y}^{2}}}{{{x}^{2}}} \right)={{\tan }^{-1}}(x)-\frac{\pi }{4}\]

    Correct Answer: B

    Solution :

    \[\int_{{}}^{{}}{\frac{ydy}{1+{{y}^{2}}}\,=\int_{{}}^{{}}{\frac{1+x+{{x}^{2}}}{x(1+{{x}^{2}})}dx;}}\] \[\Rightarrow \,\,\frac{1}{2}\,\ln \,(1+{{y}^{2}})\,={{\tan }^{-1}}\,x+\ln x\,+C\] \[\Rightarrow \,\ln \,\frac{1+{{y}^{2}}}{{{x}^{2}}}=2\,{{\tan }^{-1}}\,x+C\]


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