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

  • question_answer
    The solution of the differential equation \[\frac{dy}{dx}=\frac{x-y+3}{2(x-y)+5}\] is

    A)                 \[2(x-y)+\log (x-y)=x+c\]

    B)                 \[2(x-y)-\log (x-y+2)=x+c\]

    C)                 \[2(x-y)+\log (x-y+2)=x+c\]

    D)                 None of these

    Correct Answer: C

    Solution :

                       Let \[x-y=v\]and \[\frac{dy}{dx}=1-\frac{dv}{dx},\]thus the equation reduces to \[\frac{dv}{dx}=\frac{v+2}{2v+5}\]Þ\[\int_{{}}^{{}}{\frac{2v+5}{v+2}}dv=\int_{{}}^{{}}{dx}\]                    Þ \[\int_{{}}^{{}}{\left[ 2+\frac{1}{(v+2)} \right]}dv=\int_{{}}^{{}}{dx}\] Þ \[2v+\log (v+2)=x+c\]                                 or \[2(x-y)+\log (x-y+2)=x+c\].


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