JEE Main & Advanced Mathematics Differential Equations Question Bank Application of differnetial equations

  • question_answer
    The equation of the curve that passes through the point \[(1,\,2)\] and satisfies the differential equation \[\frac{dy}{dx}=\frac{-2xy}{({{x}^{2}}+1)}\]is

    A)                 \[y({{x}^{2}}+1)=4\]      

    B)                 \[y({{x}^{2}}+1)+4=0\]

    C)                 \[y({{x}^{2}}-1)=4\]        

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[\frac{dy}{dx}=\frac{-2xy}{({{x}^{2}}+1)}\] Þ \[\frac{dy}{y}=-\frac{2x}{{{x}^{2}}+1}dx\]         On integrating, we get         \[\log y=-\log (1+{{x}^{2}})+\log c\]Þ\[y(1+{{x}^{2}})=c\]         Since curve passes through (1, 2), we have         \[c=2(1+{{1}^{2}})\] Þ \[c=4\]                                 Hence solution is \[y({{x}^{2}}+1)=4\].


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