JEE Main & Advanced Mathematics Differential Equations Question Bank Homogeneous differential equations

  • question_answer
    Solution of differential equation \[2xy\frac{dy}{dx}={{x}^{2}}+3{{y}^{2}}\] is [MP PET 1993]

    A)                 \[{{x}^{3}}+{{y}^{2}}=p{{x}^{2}}\]    

    B)                 \[\frac{{{x}^{2}}}{2}+\frac{{{y}^{3}}}{x}={{y}^{2}}+p\]

    C)                 \[{{x}^{2}}+{{y}^{3}}=p{{x}^{2}}\]    

    D)                 \[{{x}^{2}}+{{y}^{2}}=p{{x}^{3}}\]

    Correct Answer: D

    Solution :

                       It is homogeneous equation \[\frac{dy}{dx}=\frac{{{x}^{2}}+3{{y}^{2}}}{2xy}\]         Put \[y=vx\] and \[\frac{dy}{dx}=v+x\frac{dv}{dx}\]         So, we get \[x\frac{dv}{dx}=\frac{1+{{v}^{2}}}{2v}\]         Þ \[\frac{2vdv}{1+{{v}^{2}}}=\frac{dx}{x}\]                                 On integrating, we get \[{{x}^{2}}+{{y}^{2}}=p{{x}^{3}}\]. (where p is a constant)


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