JEE Main & Advanced Mathematics Differential Equations Question Bank Linear defferential equations

  • question_answer
    The solution of the equation \[x\frac{dy}{dx}+3y=x\] is

    A)                 \[{{x}^{3}}y+\frac{{{x}^{4}}}{4}+c=0\]

    B)                 \[{{x}^{3}}y=\frac{{{x}^{4}}}{4}+c\]

    C)                 \[{{x}^{3}}y+\frac{{{x}^{4}}}{4}=0\]     

    D)                 None of these

    Correct Answer: B

    Solution :

                       \[x\frac{dy}{dx}+3y=x\] Þ \[\frac{dy}{dx}+\frac{3y}{x}=1\]         It is in the form of \[\frac{dy}{dx}+Py=Q\]         So, I.F. \[={{e}^{\int_{{}}^{{}}{Pdx}}}={{e}^{3}}^{\int_{{}}^{{}}{\frac{1}{x}dx}}={{e}^{3\log x}}={{x}^{3}}\]         Hence required solution is                                 \[y+{{x}^{2}}+2x+2=c{{e}^{x}}\] Þ \[y{{x}^{3}}=\frac{{{x}^{4}}}{4}+c\].


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