CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

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

    A)  order 1, degree 2           

    B)  order 1, degree 3

    C)  order 2, degree 3           

    D)  order 2, degree 2

    E)  order 1, degree 1

    Correct Answer: B

    Solution :

    \[{{y}^{2}}=2c(x+\sqrt{c})\]                         ?.. (i) Differentiating w.r.t.\[x,\] \[2y\frac{dy}{dx}=2c\] \[\Rightarrow \]               \[c=y\frac{dy}{dx}\] On putting this value in Eq. (i), \[{{y}^{2}}=2x.y\frac{dy}{dx}+2y\frac{dy}{dx}\sqrt{y\frac{dy}{dx}}\] \[2y\frac{dy}{dx}\sqrt{y\frac{dy}{dx}}={{y}^{2}}-2xy\frac{dy}{dx}\] Squaring on both sides, \[4{{y}^{2}}{{\left( \frac{dy}{dx} \right)}^{2}}\left( y.\frac{dy}{dx} \right)={{\left\{ {{y}^{2}}-2xy\frac{dy}{dx} \right\}}^{2}}\] \[4{{y}^{3}}{{\left( \frac{dy}{dx} \right)}^{3}}={{y}^{2}}+4{{x}^{2}}{{y}^{2}}{{\left( \frac{dy}{dx} \right)}^{2}}-2x{{y}^{3}}\left( \frac{dy}{dx} \right)\] \[4y{{\left( \frac{dy}{dx} \right)}^{3}}=-4{{x}^{2}}{{\left( \frac{dy}{dx} \right)}^{2}}+2xy\left( \frac{dy}{dx} \right)-{{y}^{2}}=0\] Hence, order\[\to 1,\]degree\[\to 3\]


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