BCECE Engineering BCECE Engineering Solved Paper-2014

  • question_answer
    If ; \[y={{x}^{2}}+\frac{1}{{{x}^{2}}+\frac{1}{{{x}^{2}}+\frac{1}{{{x}^{2}}+......\infty }}},\] \[\frac{dy}{dx}\], is equal to

    A) \[\frac{2xy}{2y-{{x}^{2}}}\]         

    B) \[\frac{xy}{y+{{x}^{2}}}\]

    C) \[\frac{xy}{y-{{x}^{2}}}\]                             

    D) \[\frac{2x}{2+\frac{{{x}^{2}}}{y}}\]

    Correct Answer: A

    Solution :

    Given equation can be written as \[y={{x}^{2}}+\frac{1}{y}\Rightarrow {{y}^{2}}={{x}^{2}}y+1\] On differentiating w. r. t x,  we get \[2y\frac{dy}{dx}={{x}^{2}}\frac{dy}{dx}+2xy+0\] \[\Rightarrow \frac{dy}{dx}(2y-{{x}^{2}})=2xy\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{2xy}{2y-{{x}^{2}}}\]                


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