JEE Main & Advanced Sample Paper JEE Main Sample Paper-16

  • question_answer
    Let \[f(x)=\frac{x-1}{4}+\frac{{{(x-1)}^{3}}}{12}+\frac{{{(x-1)}^{5}}}{20}+\frac{{{(x-1)}^{7}}}{28}\]?.\[\infty \] for \[x\in \] (0. 2), then \[f'\left( \frac{3}{2} \right)\] is equal to

    A) \[\frac{1}{2}\]                                   

    B) \[\frac{1}{4}\]

    C) \[\frac{1}{5}\]                                   

    D) \[\frac{1}{3}\]

    Correct Answer: D

    Solution :

    \[f(x)=\frac{1}{4}\left( (x-1)+\frac{{{(x-1)}^{3}}}{3}+\frac{{{(x-1)}^{5}}}{5}+\frac{{{(x-1)}^{7}}}{7}....... \right)\]\[=\frac{1}{4}\cdot \frac{1}{2}\ln \left( \frac{1+(x-1)}{1-(x-1)} \right)=\frac{1}{8}\ln \left( \frac{x}{2-x} \right)\] \[f'(x)=\frac{1}{1x(2-x)}\Rightarrow f'\left( \frac{3}{2} \right)=\frac{1}{3}\]


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