JEE Main & Advanced Mathematics Sequence & Series Question Bank Logarithmic series

  • question_answer
    \[{{\log }_{e}}\sqrt{\frac{1+x}{1-x}}=\]

    A) \[{{\log }_{e}}\frac{1}{2}\]

    B) \[2\,\left[ x+\frac{{{x}^{3}}}{3}+\frac{{{x}^{5}}}{5}+.....\infty  \right]\]

    C) \[2\,\left[ {{x}^{2}}+\frac{{{x}^{4}}}{4}+\frac{{{x}^{6}}}{6}+.....\infty  \right]\]

    D) None of these

    Correct Answer: A

    Solution :

    \[{{\log }_{e}}\sqrt{\frac{1+x}{1-x}}=\frac{1}{2}{{\log }_{e}}\frac{1+x}{1-x}\] \[=\frac{1}{2}.2\left\{ x+\frac{{{x}^{3}}}{3}+\frac{{{x}^{5}}}{5}+...... \right\}=x+\frac{{{x}^{3}}}{3}+\frac{{{x}^{5}}}{5}+......\]


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