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

  • question_answer
    Solution of the differential equation, \[y\,dx-x\,dy+x{{y}^{2}}dx=0\] can be

    A)                 \[2x+{{x}^{2}}y=\lambda y\]        

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

    C)                 \[2y-{{y}^{2}}x=\lambda y\]          

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[\frac{ydx-xdy}{{{y}^{2}}}=-xdx\] Þ \[d\left( \frac{x}{y} \right)=-xdx\]                    Integrating both side, we get \[\frac{x}{y}=-\frac{{{x}^{2}}}{2}+c\]                                 Þ \[2x+{{x}^{2}}y=2cy\] Þ \[2x+{{x}^{2}}y=\lambda y\]     [\[\lambda =2c\]]


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