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

  • question_answer
    Solution of the equation \[(1-{{x}^{2}})dy+xydx=x{{y}^{2}}dx\] is [DSSE 1989]

    A)                 \[{{(y-1)}^{2}}(1-{{x}^{2}})=0\]

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

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

    D)                 None of these

    Correct Answer: B

    Solution :

                       \[(1-{{x}^{2}})dy+xydx=x{{y}^{2}}dx\]                    Þ \[(1-{{x}^{2}})dy=xy(y-1)dx\] Þ \[\frac{1}{y(y-1)}dy=\frac{x}{(1-{{x}^{2}})}dx\]                    Now on integrating both sides, we get                    \[\log (y-1)-\log y=-\frac{1}{2}\log (1-{{x}^{2}})+\log c\]                    or \[2\log (y-1)+\log (1-{{x}^{2}})=\log {{y}^{2}}{{c}^{2}}\]                                 Hence the solution is \[{{(y-1)}^{2}}(1-{{x}^{2}})={{c}^{2}}{{y}^{2}}\].


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