KVPY Sample Paper KVPY Stream-SX Model Paper-31

  • question_answer
    Solution of differential equation \[{{({{x}^{2}}+1)}^{2}}\frac{dy}{dx}+2({{x}^{2}}+1)y=1\] is:

    A) \[y=\frac{{{\tan }^{-1}}x}{{{x}^{2}}+1}+C\]

    B) \[y={{\tan }^{-1}}x+C\]

    C) \[y({{x}^{2}}+1)={{\tan }^{-1}}x+C\]

    D) \[y(ta{{n}^{-1}}x={{x}^{2}}+C\]

    Correct Answer: C

    Solution :

    \[{{({{x}^{2}}+1)}^{2}}\frac{dy}{dx}+2x({{x}^{2}}+1)y=1\]
    \[\frac{dy}{dx}+\frac{2x}{{{x}^{2}}+1}y=\frac{1}{{{({{x}^{2}}+1)}^{2}}}\]
    Linear D.E.,
    \[I.F.={{e}^{\int{\frac{2x}{{{x}^{2}}+1}dx}}}={{e}^{\ell n({{x}^{2}}+1)}}={{x}^{2}}+1\]
    \[\therefore \]      \[y(I.F.)=\int{Q(IF)dx}\]
    \[y({{x}^{2}}+1)=\int{\frac{1}{{{({{x}^{2}}+1)}^{2}}}}({{x}^{2}}+1)dx\]
    \[y({{x}^{2}}+1)={{\tan }^{-1}}x+C.\]


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