CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2000

  • question_answer
    If\[xy=x+y,\]then\[\left( \frac{dy}{dx} \right)\]is equal to:

    A)  \[\frac{xy}{(1-x)}\]        

    B)         \[\frac{(1+y)}{(1-x)}\]

    C)  \[\frac{y}{(1-xy)}\]        

    D)         \[\frac{-1}{{{(x-1)}^{2}}}\]

    E)  \[\frac{1}{({{x}^{2}}-1)}\]

    Correct Answer: D

    Solution :

    \[xy=x+y\Rightarrow xy-y=x\] \[\Rightarrow \] \[y(x-1)=x\] \[\Rightarrow \] \[yx=x+y\] On differentiating w.r.t.\[x,\]we get                 \[x\frac{dy}{dx}+y=1+\frac{dy}{dx}\] \[\Rightarrow \]               \[\frac{dy}{dx}(x-1)=1-y\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{1-y}{x-1}=\frac{1-\frac{x}{x-1}}{x-1}\]                                 \[=\frac{x-1-x}{{{(x-1)}^{2}}}=\frac{-1}{{{(x-1)}^{2}}}\]


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