JEE Main & Advanced Mathematics Differential Equations Question Bank Miscellaneous differential equations

  • question_answer
    The solution of the differential equation \[x\frac{{{d}^{2}}y}{d{{x}^{2}}}=1\], given that \[y=1,\ \frac{dy}{dx}=0\]when \[x=1\], is

    A)            \[y=x\log x+x+2\]                  

    B)            \[y=x\log x-x+2\]

    C)            \[y=x\log x+x\]                       

    D)            \[y=x\log x-x\]

    Correct Answer: B

    Solution :

                       \[x\frac{{{d}^{2}}y}{d{{x}^{2}}}=1\] Þ \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\frac{1}{x}\]Þ \[\frac{dy}{dx}=\log x+{{c}_{1}}\]                    Þ \[y=x\log x-x+{{c}_{1}}x+{{c}_{2}}\]        (on integrating twice)                    Given \[y=1\]and \[\frac{dy}{dx}=0\]at \[x=1\]Þ \[{{c}_{1}}=0\]and \[{{c}_{2}}=2\] Therefore, the required solution is \[y=x\log x-x+2\].


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