JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    lf\[\sqrt{x}+\sqrt{y}=10\], find\[\frac{dx}{dy}\]at\[y=4\].

    A) \[4\]                                     

    B) \[-3\]

    C) \[-4\]                                    

    D) \[3\]

    Correct Answer: C

    Solution :

    \[\sqrt{x}+\sqrt{y}=10\]                 \[\frac{1}{2\sqrt{x}}\frac{dx}{dy}+\frac{1}{2\sqrt{y}}=0\] \[\Rightarrow \]               \[\frac{dx}{dy}=-\frac{\sqrt{x}}{\sqrt{y}}=-\frac{10-\sqrt{y}}{\sqrt{y}}\] \[\Rightarrow \]               \[\frac{dx}{dy}=\frac{\sqrt{y}-10}{\sqrt{y}}\] \[\Rightarrow \]               \[{{\left( \frac{dy}{dx} \right)}_{y=4}}=\frac{2-10}{2}=\frac{-8}{2}=-4\]


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