BCECE Engineering BCECE Engineering Solved Paper-2012

  • question_answer
    The sum of the series \[1+\frac{1}{3}.\frac{1}{4}+\frac{1}{5}.\frac{1}{{{4}^{2}}}+\frac{1}{7}.\frac{1}{{{4}^{3}}}+\,.....\infty \]is

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

    B)         \[{{\log }_{e}}2\]                            

    C)         \[{{\log }_{e}}3\]                            

    D)         \[{{\log }_{e}}4\]

    Correct Answer: C

    Solution :

    Since,\[\log (1+x)-\log (1-x)\] \[=2\left[ x+\frac{{{x}^{3}}}{3}+\frac{{{x}^{5}}}{5}+...\infty  \right]\] Put \[x=\frac{1}{2}\]on both sides, we get           \[\log \left( \frac{3}{2} \right)-\log \left( \frac{1}{2} \right)=2\left( \frac{1}{2}+\frac{1}{3}.\frac{1}{{{2}^{3}}}+\frac{1}{5}.\frac{1}{{{2}^{5}}}+...\infty  \right)\] \[\Rightarrow \]               \[\log 3=1+\frac{1}{3}.\frac{1}{4}+\frac{1}{5}.\frac{1}{{{4}^{2}}}+...\]


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