J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    Solve \[\frac{dy}{dx}+\frac{y}{x}={{x}^{3}}\]

    A)  \[y=\frac{{{x}^{4}}}{5}+Cx\]

    B)  \[y=\frac{{{x}^{3}}}{3}+Cx\]

    C)  \[y=\frac{{{x}^{3}}}{3}+C\]

    D)  \[y=\frac{{{x}^{4}}}{4}+x\]

    E)  None of these

    Correct Answer: E

    Solution :

    We have,  \[\frac{dy}{dx}+\frac{y}{x}={{x}^{3}}\] On comparing with \[\frac{dy}{dx}+py=Q,\] we get \[P=\frac{1}{x},Q={{x}^{3}}\] \[\therefore \] \[IF={{e}^{\int{\frac{1}{x}dx}}}={{e}^{{{\log }_{e}}x}}=x\] Now, solution of given differential equation is \[y.If=\int{!Q.\,IF\,dx+C}\] \[\Rightarrow \] \[yx=\int{{{x}^{3}}.x\,dx+C}\] \[\Rightarrow \] \[yx=\int{{{x}^{4}}\,dx+C}\] \[\Rightarrow \] \[yx=\frac{{{x}^{5}}}{5}+C\] \[\Rightarrow \] \[y=\frac{{{x}^{4}}}{5}+\frac{C}{x}\]


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