CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2006

  • question_answer
    An integrating factor of the differential equation, \[(1+y+{{x}^{2}}y)dx+(x+{{x}^{3}})dy=0\]is:

    A)  \[\log x\]           

    B)         \[x\]

    C)  \[{{e}^{x}}\]                     

    D)         \[\frac{1}{x}\]

    E)  \[\frac{-1}{x}\]

    Correct Answer: B

    Solution :

    \[dy(x+{{x}^{3}})=-dx(1+y+{{x}^{2}}y)\] \[\Rightarrow \]               \[\frac{dy}{dx}=-\frac{1+y+{{x}^{2}}y}{x+{{x}^{3}}}\] \[\Rightarrow \]               \[\frac{dy}{dx}+\frac{y{{(1+x)}^{2}}}{x(1+{{x}^{2}})}=-\frac{1}{x(1+{{x}^{2}})}\] \[\Rightarrow \]               \[\frac{dy}{dx}+\frac{y}{x}=-\frac{1}{x(1+{{x}^{2}})}\] \[\therefore \]  \[IF={{e}^{\int{\frac{1}{x}dx}}}={{e}^{\log x}}=x\]


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