JEE Main & Advanced AIEEE Solved Paper-2003

  • question_answer
    The solution of the differential equation \[(1+{{y}^{2}})+(x-{{e}^{{{\tan }^{-1}}}}y)\frac{dy}{dx}=0\], is     AIEEE  Solved  Paper-2003

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

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

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

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

    Correct Answer: B

    Solution :

    \[(1+{{y}^{2}})+(x-{{e}^{{{\tan }^{-1}}y}})\frac{dy}{dx}=0\] \[\Rightarrow \]   \[(1+{{y}^{2}})\frac{dx}{dy}+x={{e}^{{{\tan }^{-1}}y}}\] \[\Rightarrow \]   \[\frac{dx}{dy}+\frac{1}{1+{{y}^{2}}}x=\frac{{{e}^{{{\tan }^{-1}}y}}}{1+{{y}^{2}}}\]             \[IF={{e}^{\int_{{}}^{{}}{P\,dy}}}={{e}^{\int_{{}}^{{}}{\frac{1}{1+{{y}^{2}}}dy}}}={{e}^{{{\tan }^{-1}}y}}\] Therefore, required solution is                     \[x\,.\,\,{{e}^{{{\tan }^{-1}}y}}=\int{{{e}^{{{\tan }^{-1}}y}}.\frac{{{e}^{{{\tan }^{-1}}y}}}{1+{{y}^{2}}}dy+{{k}_{1}}}\] \[\Rightarrow \]   \[x{{e}^{{{\tan }^{-1}}y}}=\int_{{}}^{{}}{\frac{{{e}^{2{{\tan }^{-1}}y}}}{1+{{y}^{2}}}\,dy+{{k}_{1}}}\] \[\Rightarrow \]   \[x{{e}^{{{\tan }^{-1}}y}}=\frac{1}{2}{{e}^{2{{\tan }^{-1}}y}}+{{k}_{1}}\] \[\Rightarrow \]   \[2\,x\,{{e}^{{{\tan }^{-1}}y}}={{e}^{2{{\tan }^{-1}}y}}+k\]          


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