JEE Main & Advanced JEE Main Online Paper (Held on 9 April 2013)

  • question_answer
                    If  \[x=\int\limits_{0}^{y}{\frac{dt}{1+{{t}^{2}}},}\] then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}\] is equal to:                   JEE Main Online Paper (Held On 09 April 2013)

    A)                 \[y\]                

    B)                 \[\sqrt{1+{{y}^{2}}}\]                

    C)                 \[\frac{y}{\sqrt{1+{{y}^{2}}}}\]                

    D)                 \[{{y}^{2}}\]

    Correct Answer: A

    Solution :

                    \[x=\int_{0}^{y}{\frac{dt}{\sqrt{1+{{t}^{2}}}},}\] by Leibnitz rule, we get                 \[1=\frac{1}{\sqrt{1+{{y}^{2}}}}.\,\frac{dy}{dx}\] \[\Rightarrow \]               \[\frac{dy}{dx}=\sqrt{1+{{y}^{2}}}\] \[\Rightarrow \]               \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\frac{y}{\sqrt{1+{{y}^{2}}}}\cdot \,\frac{dy}{dx}\] \[\therefore \]  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\,\frac{y}{\sqrt{1+{{y}^{2}}}}\cdot \,\sqrt{1+{{y}^{2}}}=y\]                


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