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

  • question_answer
    Solution of \[ydx-xdy={{x}^{2}}ydx\]is         [MP PET 1999]

    A)                 \[y{{e}^{{{x}^{2}}}}=c{{x}^{2}}\]         

    B)                 \[y{{e}^{-{{x}^{2}}}}=c{{x}^{2}}\]

    C)                 \[{{y}^{2}}{{e}^{{{x}^{2}}}}=c{{x}^{2}}\]      

    D)                 \[{{y}^{2}}{{e}^{-{{x}^{2}}}}=c{{x}^{2}}\]

    Correct Answer: C

    Solution :

                       Given equation can be written as \[\left( \frac{1-{{x}^{2}}}{x} \right)dx=\frac{dy}{y}\]        After integration, we get \[\log x-\frac{{{x}^{2}}}{2}=\log y+\log c\]        Þ \[\log {{x}^{2}}-\log {{y}^{2}}+\log c={{x}^{2}}\]Þ\[\log \frac{c{{x}^{2}}}{{{y}^{2}}}={{x}^{2}}\]                 Þ \[\frac{c{{x}^{2}}}{{{y}^{2}}}={{e}^{x}}^{2}\]Þ\[c{{x}^{2}}={{y}^{2}}{{e}^{{{x}^{2}}}}\].


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