BCECE Engineering BCECE Engineering Solved Paper-2011

  • question_answer
    The differential equation representing the family of curves \[{{y}^{2}}=2x(x+\sqrt{c}),\]where c is a positive perimeter, is of

    A)  order 1, degree 3              

    B)         order 2, degree 2              

    C)         degree 3, order 3              

    D)         degree 4, order 4

    Correct Answer: A

    Solution :

    Given family of curves \[{{y}^{2}}=2c(x+\sqrt{c})\]                ?(i) On differentiating both sides, we get                 \[2y\frac{dy}{dx}=2c(1+0)\Rightarrow c=y\frac{dy}{dx}\]                 From Eq. (i), \[{{y}^{2}}=2y\frac{dy}{dx}\left\{ x+{{\left( y\frac{dy}{dx} \right)}^{1/2}} \right\}\]                 \[\Rightarrow \]    \[\left( {{y}^{2}}-2xy\frac{dy}{dx} \right)=2{{\left( y\frac{dy}{dx} \right)}^{3/2}}\]                  On squaring both sides, we get                 \[{{\left( {{y}^{2}}-2xy\frac{dy}{dx} \right)}^{2}}=4{{\left( y\frac{dy}{dx} \right)}^{3}}\] So, order 1 and degree 3.


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