CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

  • question_answer
    The equation of a curve passing through the origin and satisfying the differential equation \[\frac{dy}{dx}={{(x-y)}^{2}}\]is:

    A)  \[{{e}^{2x}}(1-x+y)=1+x-y\]

    B)  \[{{e}^{2x}}(1+x-y)=1-x+y\]

    C)  \[{{e}^{2x}}(1-x+y)+(1+x-y)=0\]

    D)  \[{{e}^{2x}}(1+x+y)=1-x+y\]

    E)  none of the above

    Correct Answer: A

    Solution :

    The given differential equation is \[\frac{dy}{dx}={{(x-y)}^{2}}\] Let           \[x-y=t\] \[\Rightarrow \]               \[1-\frac{dy}{dx}=\frac{dt}{dx}\] \[\Rightarrow \]               \[\frac{dy}{dx}=1-\frac{dt}{dx}\] \[\therefore \]  \[1-\frac{dt}{dx}={{t}^{2}}\] \[\Rightarrow \]               \[(1-{{t}^{2}})=\frac{dt}{dx}\] On integrating both sides \[\Rightarrow \]               \[\int{\frac{1}{1-{{t}^{2}}}}dt=\int{1\,}dx\] \[\Rightarrow \]               \[\frac{1}{2}\log \left( \frac{1+t}{1-t} \right)=x+c\] \[\Rightarrow \]               \[\left( \frac{1+t}{1-t} \right)={{e}^{2x+2c}}\] \[\Rightarrow \]               \[\frac{1+x-y}{1-x+y}=A{{e}^{2x}}\] \[\because \]It passes through origin \[\therefore \]  \[A=1\] \[\therefore \]Required curve is                 \[(1+x-y)={{e}^{2x}}(1-x+y)\]


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