JEE Main & Advanced Mathematics Sequence & Series Question Bank Self Evaluation Test - Sequences and Series

  • question_answer
    The value of the infinite product \[{{6}^{\frac{1}{2}}}\times {{6}^{\frac{1}{2}}}\times {{6}^{\frac{3}{8}}}\times {{6}^{\frac{1}{4}}}....\] is

    A) 6

    B) 36

    C) 216

    D) \[\infty \]

    Correct Answer: C

    Solution :

    [c] \[X={{6}^{\left( \frac{1}{2}+\frac{1}{2}+\frac{3}{8}+\frac{1}{4}+..... \right)}}\] \[={{6}^{\left[ \left( 1\times \frac{1}{2} \right)+\left( 2\times \frac{1}{4} \right)+\left( 3\times \frac{1}{8} \right)+\left( 4\times \frac{1}{16} \right)+...... \right]}}\] \[\because \] It is arithmetic-geometric progression, \[\therefore a=\frac{1}{2};\,\,\,d=1\] & \[r=\frac{1}{2}\] \[\Rightarrow \,\,\,\,\,\,\,\,X={{6}^{\left[ \frac{a}{1-r}+\frac{dr}{{{(1-r)}^{2}}} \right]}}={{6}^{\left[ \frac{\frac{1}{2}}{1-\frac{1}{2}}+\frac{1\times \frac{1}{2}}{{{(1-\frac{1}{2})}^{2}}} \right]}}={{6}^{3}}=216\]


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