CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    Solution   of   the   differential   equation \[\frac{dy}{dx}+\frac{y}{x}=\sin x\]is:

    A)  \[x(y+\cos x)=\sin x+c\]

    B)  \[x(y-\cos x)=\sin x+c\]

    C)  \[x(y\cos x)=\sin x+c\]

    D)  \[x(y-\cos x)=\cos x+c\]

    E)  \[x(y+\cos x)=\cos x+c\]

    Correct Answer: A

    Solution :

    \[\because \]     \[\frac{dy}{dx}+\frac{y}{x}=\sin x\] Here,\[P=\frac{1}{x}\]and \[Q=\sin x\] \[\therefore \] \[IF={{e}^{\int{p}\,dx}}={{e}^{\int{1/x}\,dx}}=x\] \[\therefore \]  Solution is \[y(IF)=\int{Q(IF)}\,dx+c\] \[\Rightarrow \]               \[y.x=\int{x\,\sin x\,dx+c}\] \[\Rightarrow \]               \[xy=-x\cos x+\sin x+c\] \[\Rightarrow \] \[x(y+\cos x)=\sin x+c\]


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