JEE Main & Advanced Sample Paper JEE Main Sample Paper-33

  • question_answer
    The solution of the differential equation \[y\,\ell \,n\,y+xy'=0,\] where \[y(1)\,\,=e,\] is

    A)  \[x{{(\ell \,n\,y)}^{2}}=1\]

    B)  \[x(\ell \,n\,y)=1\]

    C)  \[{{(\ell \,n\,y)}^{2}}=x\]

    D)  \[(x+\ell \,n\,y)=2\]

    Correct Answer: B

    Solution :

    \[x\frac{dy}{dx}+y(\ln \,y)=0\,\Rightarrow \,\int{\frac{dx}{x}+\int{\frac{dy}{y(\ln \,y)}}}=C;\] \[\ln \,(x\,\ln \,y\,)=C.\]. If \[x=1\] then \[y=e\]  \[\Rightarrow \,\ln \,(\ln \,e)\,=C\Rightarrow \,C=0\]


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