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

  • question_answer
    The solution of the differential equation \[xy\frac{dy}{dx}=\frac{(1+{{y}^{2}})(1+x+{{x}^{2}})}{(1+{{x}^{2}})}\] is                 [AISSE 1983]

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

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

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

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

    Correct Answer: B

    Solution :

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


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