CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    The sum of the series\[lo{{g}_{9}}3+lo{{g}_{27}}3-lo{{g}_{81}}3+lo{{g}_{243}}3-.....\]is

    A)  \[1-lo{{g}_{e}}2\]       

    B)         \[1+lo{{g}_{e}}2\]

    C) \[lo{{g}_{e}}2\]                

    D)         \[lo{{g}_{e}}3\]

    E)  \[1+lo{{g}_{e}}3\]

    Correct Answer: C

    Solution :

    Let\[S={{\log }_{9}}3+{{\log }_{27}}3-{{\log }_{81}}3+{{\log }_{243}}3-....\]          \[={{\log }_{{{3}^{2}}}}3+{{\log }_{{{3}^{3}}}}3-{{\log }_{{{3}^{4}}}}3+{{\log }_{{{3}^{5}}}}3-....\] \[=\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+\frac{1}{5}-....+1-1\]                 \[=1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+\frac{1}{5}-....\]                 \[={{\log }_{e}}(1+1)={{\log }_{e}}2\]


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