CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2010

  • question_answer
    The solution of the differential equation\[\frac{dy}{dx}+1={{e}^{x+y}}\]is

    A)  \[x+{{e}^{x+y}}=c\]                      

    B)  \[x-{{e}^{x+y}}=c\]

    C)  \[x+{{e}^{-(x+y)}}=c\]

    D)         \[x-{{e}^{-(x+y)}}=c\]

    E)  \[x{{e}^{x+y}}+y=c\]

    Correct Answer: C

    Solution :

    Given differential equation is \[\frac{dy}{dx}+1={{e}^{x+y}}\]                   ...(i) Put \[x+y=t\] Differentiating w.r.t.\[x,\]we get                 \[1+\frac{dy}{dx}=\frac{dt}{dx}\]                             ?..(ii) From Eqs. (i) and (ii) \[\frac{dt}{dx}={{e}^{t}}\] \[\Rightarrow \]               \[{{e}^{-t}}dt=dx\] \[\Rightarrow \]               \[-{{e}^{-t}}=x+c\] \[\Rightarrow \]               \[x+{{e}^{-t}}=c\] \[\Rightarrow \]               \[x+{{e}^{-(x+y)}}=c\]


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