12th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-7

  • question_answer
    The solution of the differential equation, \[(1+{{y}^{2}})-\left( x+{{e}^{{{\tan }^{-1}}y}} \right)\frac{dy}{dx}=0\].is

    A)  \[(x-2)=k{{e}^{{{\tan }^{-1}}y}}\]               

    B)  \[2x{{e}^{{{\tan }^{-1}}y}}={{e}^{2{{\tan }^{-1}}y}}+k\]  

    C) \[x.{{e}^{-{{\tan }^{-1}}y}}=ta{{n}^{-1y}}+k\]                      

    D)  \[x.{{e}^{2{{\tan }^{-1}}y}}=ta{{n}^{-1y}}+k\]

    Correct Answer: C

    Solution :

    [c] \[(1+{{y}^{2}})-(x+{{e}^{{{\tan }^{-1}}y}})\frac{dy}{dx}=0\] \[\Rightarrow (1+{{y}^{2}})\frac{dy}{dx}-x={{e}^{{{\tan }^{-1}}y}}\] \[\Rightarrow \frac{dy}{dx}-\frac{1}{1+{{y}^{2}}}x=\frac{{{e}^{{{\tan }^{-1}}y}}}{1+{{y}^{2}}}\] \[IF={{e}^{\int{pdy}}}={{e}^{\int{\frac{-1}{1+{{y}^{2}}}dy}}}={{e}^{-{{\tan }^{-1}}y}}\] \[\therefore \]The solution is \[x.{{e}^{-{{\tan }^{-1}}y}}=\int{{{e}^{-{{\tan }^{-1}}y}}}.\frac{{{e}^{-{{\tan }^{-1}}y}}}{1+{{y}^{2}}}.dy+k\] Or \[x.{{e}^{-{{\tan }^{-1}}y}}=\int{\frac{1}{1+{{y}^{2}}}}.dy+k\] Or \[x.{{e}^{-{{\tan }^{-1}}y}}={{\tan }^{-1}}y+k\]


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