JEE Main & Advanced Mathematics Differential Equations Question Bank Self Evaluation Test - Differential Equations

  • question_answer
    Solution of the differential equation\[\frac{dx}{dy}-\frac{x\,\,\log \,\,x}{1+\log \,\,x}=\frac{{{e}^{y}}}{1+\log \,\,x'}\] if \[y(1)=0\], is

    A) \[{{x}^{x}}={{e}^{y{{e}^{y}}}}\]

    B) \[{{e}^{y}}={{x}^{{{e}^{y}}}}\]

    C) \[{{x}^{x}}=y{{e}^{^{y}}}\]

    D) None of these

    Correct Answer: A

    Solution :

    [a] \[(1+logx)\frac{dx}{dy}-x\log x={{e}^{y}}\] putting x log \[x\log x=t\Rightarrow (1+logx)dx=dt\] \[\therefore \frac{dt}{dy}-t={{e}^{y}}\] Now, I.F. \[={{e}^{\int{-1dy}}}={{e}^{-y}}\] \[\Rightarrow t{{e}^{-y}}=\int{{{e}^{-y}}{{e}^{y}}dy+C}\] \[\Rightarrow t=C{{e}^{y}}+y{{e}^{y}}\Rightarrow x\log x=(C+y){{e}^{y}},\] Since, \[y(1)=0,\] Then \[0=(C+0)1\Rightarrow C=0\] \[\therefore y{{e}^{y}}=x\log x\Rightarrow {{x}^{x}}={{e}^{y{{e}^{y}}}}\]


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