JEE Main & Advanced Mathematics Differential Equations Question Bank Variable Separable type differential equations

  • question_answer
    The general solution of the differential equation \[ydx\,+(1+{{x}^{2}}){{\tan }^{-1}}xdy=0,\] is     [MP PET 1995]

    A)                 \[y{{\tan }^{-1}}x=c\]      

    B)                 \[x{{\tan }^{-1}}y=c\]

    C)                 \[y+{{\tan }^{-1}}x=c\]   

    D)                 \[x+{{\tan }^{-1}}y=c\]

    Correct Answer: A

    Solution :

                       \[ydx+(1+{{x}^{2}}){{\tan }^{-1}}xdy=0\]                    Þ \[\int_{{}}^{{}}{\frac{dx}{(1+{{x}^{2}}){{\tan }^{-1}}x}}=-\int_{{}}^{{}}{\frac{dy}{y}}\]                    Þ \[\frac{1}{{{2}^{x}}}-\frac{1}{{{2}^{y}}}=\frac{{{c}_{1}}}{\log 2}=c\]                                 Þ \[\log (y{{\tan }^{-1}}x)+\log c=0\]Þ\[y{{\tan }^{-1}}x=c\].


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