J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    If c is a positive constant, then the differential equation of the family of the curves \[{{y}^{2}}=2c(x+\sqrt{c})\]has

    A)  order 1 and degree 3

    B)  order 1 and degree 2

    C)  order 2 and degree 1

    D)  order 3 and degree 1

    Correct Answer: A

    Solution :

    Given curve is \[{{y}^{2}}=2c(x+\sqrt{c})\] ?.(i) \[\therefore \]  \[2y\,\,\frac{dy}{dx}=2c\] \[\Rightarrow \] \[c=y\,\frac{dy}{dx}\] On putting the value of c in Eq. (i), we get \[{{y}^{2}}=2y\frac{dy}{dx}\left[ x+{{\left( y\frac{dy}{dx} \right)}^{1/2}} \right]\] \[\Rightarrow \] \[{{y}^{2}}-2yx\frac{dy}{dx}=2{{\left( y\frac{dy}{dx} \right)}^{3/2}}\] On squaring both sides, we get \[{{\left[ {{y}^{2}}-2xy\,\frac{dy}{dx} \right]}^{2}}=4{{\left[ y\frac{dy}{dx} \right]}^{3}}\] \[\therefore \]   order =1,  degree =3


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