BCECE Engineering BCECE Engineering Solved Paper-2007

  • question_answer
    If \[y\]is a function of \[x\]and \[\log (x+y)=2xy,\] then the value of \[y(0)\]is equal to

    A)  1                            

    B)         -1                          

    C)  2                            

    D)         0

    Correct Answer: A

    Solution :

    Since to find \[\frac{dy}{dx}\]at \[x=0\] \[\therefore \] At \[x=0\] \[\Rightarrow \]               \[\log (y)=0\Rightarrow y=1\] \[\therefore \]To find \[\frac{dy}{dx}\]at \[(0,1).\] On differentiating, \[\log (x+y)=2xy\]on both sides we get \[\frac{1}{x+y}\left( 1+\frac{dy}{dx} \right)=2x\frac{dy}{dx}+2y.1\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{2y(x+y)-1}{1-2(x+y)x}\] \[\therefore \]  \[{{\left( \frac{dy}{dx} \right)}_{(0,1)}}=1\]


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