JEE Main & Advanced JEE Main Paper (Held On 8 April 2017)

  • question_answer
    The curve satisfying the differential equation, \[ydx-(x+3{{y}^{2}})dy=9\]and passing through the point (1,1), also passes through the point: [JEE Online 08-04-2017]

    A) \[\left( \frac{1}{4},-\frac{1}{2} \right)\]                 

    B) \[\left( -\frac{1}{3},\frac{1}{3} \right)\]

    C) \[\left( \frac{1}{4},\frac{1}{2} \right)\]                   

    D) \[\left( \frac{1}{3},-\frac{1}{3} \right)\]

    Correct Answer: B

    Solution :

     \[ydx-xdy-3{{y}^{2}}dy=0\]                 \[\frac{dx}{dy}=\frac{x}{y}+3y\]                 \[\frac{dx}{dy}-\frac{x}{y}=3y\]                 I.f.\[{{e}^{-\int_{{}}^{{}}{\frac{1}{y}dy}}}={{e}^{-\ln y}}=\frac{1}{y}\]                 \[\therefore \]solution is                 \[\frac{x}{y}=\int_{{}}^{{}}{3y.\frac{1}{y}dy}\]                 \[\frac{x}{y}=3y+c\]pass through (1,1)                 \[\therefore \]  \[1=3+c;c=-2\]                 \[x=3{{y}^{2}}-2y\]                 (i)\[\left( \frac{1}{4},\frac{1}{2} \right)=\frac{1}{4}=\frac{3}{4}+1\]           (ii)\[-\frac{1}{3}=\frac{1}{3}-\frac{2}{3}=-\frac{1}{3}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner