JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • question_answer
        The solution of the differential equation\[y\,dx+(x+{{x}^{2}}y)dy=0\]is

    A)  \[-\frac{1}{xy}=c\]                         

    B)  \[-\frac{1}{xy}+\log y=c\]

    C)  \[\frac{1}{xy}+\log y=c\]             

    D)  \[\log y=cx\]

    Correct Answer: B

    Solution :

                    \[y\,dx+(x+{{x}^{2}}y)dy=0\] \[\Rightarrow \]               \[y\,dx+x\,dy=-{{x}^{2}}y\,dy\] \[\Rightarrow \]               \[\frac{y\,dx+x\,dy}{{{x}^{2}}{{y}^{2}}}=-\frac{1}{y}dy\] \[\Rightarrow \]               \[d\left( -\frac{1}{xy} \right)=-\frac{1}{y}dy\] On integrating, we get                 \[-\frac{1}{xy}=-\log y+c\] \[\Rightarrow \]               \[-\frac{1}{xy}+\log y=c\]


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