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

  • question_answer
    The solution of the differential equation \[\frac{dy}{dx}=\frac{(1+x)y}{(y-1)x}\]is  [AISSE 1986; AI CBSE 1982; MP PET 2004]

    A)                 \[\log xy+x+y=c\]

    B)                 \[\log \left( \frac{x}{y} \right)+x-y=c\]

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

    D)                 None of these

    Correct Answer: C

    Solution :

                       \[\frac{dy}{dx}=\frac{(1+x)y}{(y-1)x}\]can be written as                    \[\frac{y-1}{y}dy=\frac{(1+x)}{x}dx\] Þ \[\left( 1-\frac{1}{y} \right)dy=\left( 1+\frac{1}{x} \right)dx\]                                 Þ \[(y-\log y)=(x+\log x)+c\]Þ\[x-y+\log xy=c\].


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