CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    An integrating factor of the differential equation\[{{(1+x)}^{2}}\frac{dy}{dx}+xy=x\]is

    A)  \[\frac{x}{1+{{x}^{2}}}\]                              

    B)  \[\frac{1}{2}\log (1+{{x}^{2}})\]

    C)  \[\sqrt{1+{{x}^{2}}}\]   

    D)         \[x\]

    E)  \[\frac{1}{1+{{x}^{2}}}\]

    Correct Answer: C

    Solution :

    \[(1+{{x}^{2}})\frac{dy}{dx}+xy=x\] \[\Rightarrow \]               \[\frac{dy}{dx}+\frac{x}{(1+{{x}^{2}})}y=\frac{x}{(1-{{x}^{2}})}\]                 \[IF={{e}^{\int{\frac{x}{1+{{x}^{2}}}dx}}}\]                 \[={{e}^{\frac{1}{2}\log (1+{{x}^{2}})}}\]                 \[={{e}^{\log \sqrt{1+{{x}^{2}}}}}\]                 \[=\sqrt{1+{{x}^{2}}}\]


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