JEE Main & Advanced JEE Main Paper (Held On 10 April 2015)

  • question_answer
    If y(x) is the solution of the differential equation \[(x+2)\frac{dy}{dx}={{x}^{2}}+4x-9,x\ne -2\]and \[y(0)=0,\]then \[y(-4)\] is equal to : JEE Main Online Paper (Held On 10 April 2015)

    A) -1                                           

    B) 2

    C) 1                                             

    D) 0

    Correct Answer: D

    Solution :

    \[\left( x+2 \right)\frac{dy}{dx}={{x}^{2}}+4x-9x\ne -2\] \[\frac{dy}{dx}=\frac{{{x}^{2}}+4x-9}{x+2}\] \[dy=\frac{{{x}^{2}}+4x-9}{x+2}dx\] \[\int_{{}}^{{}}{dy=\int_{{}}^{{}}{\frac{{{x}^{2}}+4x-9}{x+2}}dx}\] \[y=\int_{{}}^{{}}{\left( x+2-\frac{13}{x+2} \right)dx}\] \[y=\int_{{}}^{{}}{\left( x+2 \right)dx-13\int_{{}}^{{}}{\frac{1}{x+2}dx}}\] \[y=\frac{{{x}^{2}}}{2}+2x-13\log \left| x+2 \right|+c\] Given that y = (0) = 0 \[0=-13\log z+c\] \[y=\frac{{{x}^{2}}}{2}+2x-13\log \left| x+2 \right|+13\log 2\] \[y\left( -4 \right)=8-8-13\log 2+13\log 2=0\]


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