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

  • question_answer
    If c is any arbitrary constant, then the general solution of the differential equation \[ydx-xdy=xy\,dx\] is given by  [J & K 2005]

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

    B)                 \[x=cy{{e}^{-x}}\]

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

    D)                 \[y{{e}^{x}}=cx\]

    Correct Answer: D

    Solution :

                       Given \[ydx-xdy=xydx\] Þ \[\frac{ydx-xdy}{xy}=dx\] Þ \[d\left[ \ln \left( \frac{x}{y} \right) \right]=dx\]                 Integrating both sides, we get \[\ln \frac{x}{y}+\ln c=x\] Þ \[y{{e}^{x}}=cx\].


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