JEE Main & Advanced Mathematics Differential Equations Question Bank Linear defferential equations

  • question_answer
    The solution of the differential equation \[x\log x\frac{dy}{dx}+y=2\log x\] is

    A)                 \[y=\log x+c\]       

    B)                 \[y=\log {{x}^{2}}+c\]

    C)                 \[y\log x={{(\log x)}^{2}}+c\]        

    D)                 \[y=x\log x+c\]

    Correct Answer: C

    Solution :

                       \[x\log x\frac{dy}{dx}+y=2\log x\] Þ \[\frac{dy}{dx}+\frac{1}{x\log x}y=\frac{2}{x}\]                    This is linear differential equation in y.                    \[\therefore \] I.F. \[={{e}^{\int_{x}^{{}}{\frac{1}{\log x}dx}}}={{e}^{{{\log }_{e}}{{\log }_{e}}x}}=\log x\]                    Þ \[y.\](I.F.)\[=\int_{{}}^{{}}{Q\ .\ (I.F.)\,dx}\] Þ \[y\log x=\int_{{}}^{{}}{\frac{2}{x}}.\log xdx\]                                 Þ \[y\log x={{(\log x)}^{2}}+c\].


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