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

  • question_answer
    The solution of the differential equation \[(1+{{x}^{2}})(1+y)dy+(1+x)(1+{{y}^{2}})dx=0\] is   [DSSE 1986]

    A)                 \[{{\tan }^{-1}}x+\log (1+{{x}^{2}})+{{\tan }^{-1}}y+\log (1+{{y}^{2}})=c\]

    B)                 \[{{\tan }^{-1}}x-\frac{1}{2}\log (1+{{x}^{2}})+{{\tan }^{-1}}y-\frac{1}{2}\log (1+{{y}^{2}})=c\]

    C)                 \[{{\tan }^{-1}}x+\frac{1}{2}\log (1+{{x}^{2}})+{{\tan }^{-1}}y+\frac{1}{2}\log (1+{{y}^{2}})=c\]

    D)                 None of these

    Correct Answer: C

    Solution :

                       Given equation \[(1+{{x}^{2}})(1+y)dy+(1+x)(1+{{y}^{2}})dx=0\]                    Þ \[\frac{(1+y)}{(1+{{y}^{2}})}dy=-\frac{(1+x)}{(1+{{x}^{2}})}dx\]                    Þ \[\int_{{}}^{{}}{\left[ \frac{1}{1+{{y}^{2}}}+\frac{y}{1+{{y}^{2}}} \right]}dy+\int_{{}}^{{}}{\left[ \frac{1}{1+{{x}^{2}}}+\frac{x}{1+{{x}^{2}}} \right]dx+c}=0\]                                 Þ \[{{\tan }^{-1}}y+\frac{1}{2}\log (1+{{y}^{2}})+{{\tan }^{-1}}x+\frac{1}{2}\log (1+{{x}^{2}})=c\].


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