CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2008

  • question_answer
    The differential equation \[y\,\frac{dy}{dx}+x=\]represents

    A)  a family of hyperbolas

    B)  a family of circles whose centres are on the y-axis

    C)  a family of parabolas

    D)  a family of circles whose centres are on the x-axis

    Correct Answer: D

    Solution :

    Given differential equation is \[y\,\frac{dy}{dx}+x=c\]                 \[\Rightarrow \]               \[y\,dy\,=\,(c-x)dx\] On integrating both sides, we get                 \[\frac{{{y}^{2}}}{2}=cx-\frac{{{x}^{2}}}{2}+d\] \[\Rightarrow \]               \[{{y}^{2}}+{{x}^{2}}-2cx-2d=0\] Hence, it represents a family of circles whose centres are on the x-axis.


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