JEE Main & Advanced Sample Paper JEE Main Sample Paper-22

  • question_answer
    Let  \[{{C}_{n}}=\int\limits_{\frac{1}{n+1}}^{\frac{1}{n}}{\left( \frac{{{\tan }^{-1}}(nx)}{{{\sin }^{-1}}(nx)} \right)}\,dx,\] then \[\underset{n\to \infty }{\mathop{\lim }}\,{{n}^{2}}{{C}_{n}}\] equals to

    A)  1                                

    B)  0

    C)  - 1                              

    D)  \[\frac{1}{2}\]

    Correct Answer: D

    Solution :

    \[{{C}_{n}}\,=\int\limits_{\frac{1}{n+1}}^{\frac{1}{n}}{\frac{{{\tan }^{-1}}(nx)}{{{\sin }^{-1}}(nx)}}\,dx;\,\,\,\,\]             Put \[(nx)=t\] \[\Rightarrow \,{{C}_{n}}=\frac{1}{n}\,\int\limits_{\frac{n}{n+1}}^{1}{\frac{{{\tan }^{-1}}(t)}{{{\sin }^{-1}}(t)}dt}\] \[\therefore \,\,L\,=\underset{n\to \infty }{\mathop{\lim }}\,\,{{n}^{\mathbf{2}}}.\,{{C}_{n}}=\underset{n\to \infty }{\mathop{\lim }}\,\,\,n.\,\int\limits_{\frac{n}{n+1}}^{1}{\frac{{{\tan }^{-1}}t}{{{\sin }^{-1}}t}dt}\] \[=\underset{n\to \infty }{\mathop{\lim }}\,\,\frac{\int\limits_{n}^{1}{\frac{{{\tan }^{-1}}t}{{{\sin }^{-1}}t}dt}\,}{\frac{1}{n}}\,\,\,\,\,\,\,\begin{matrix}    (0\times \infty )  \\    \left( \frac{0}{0} \right)  \\ \end{matrix}\,\,\,\,\,\,\,\,\,\] \[\therefore \] Applying Leibnitz rule and L? Hospital rule, we get limit \[=\frac{1}{2}\]


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