CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    The differential equation of the family of straight lines whose slope is equal to y-intercept is

    A)  \[(x+1)\frac{dy}{dx}-y=0\]

    B)  \[(x+1)\frac{dy}{dx}+y=0\]

    C)  \[\frac{dy}{dx}=\frac{x-1}{y-1}\]

    D)  \[\frac{dy}{dx}=\frac{x+1}{y+1}\]

    Correct Answer: A

    Solution :

    Equation of line whose slope is equal to y  intercept, is \[y=cx+c=c(x+1)\]        ...(i)                 \[\Rightarrow \]               \[\frac{dy}{dx}=c\]                                          ?..(ii) On putting the value of c from Eq. (i) in Eq. (ii), we get           \[\frac{dy}{dx}=\frac{y}{x+1}\] \[\Rightarrow \]                               \[(x+1)\frac{dy}{dx}-y=0\] Which is the required differential equation.


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