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NDA 2017
Exam
NDA
Year
2017
Subject
Mathematics
Chapter
Sequences and Series

NDA 2017 · Mathematics · Sequences and Series

The value of (1)/( _3 e)+(1)/( _3 e^2)+(1)/( _3 e^4)+ . up to...

The value of 1log⁡3e+1log⁡3e2+1log⁡3e4+…\frac{1}{\log _3 e}+\frac{1}{\log _3 e^2}+\frac{1}{\log _3 e^4}+ \ldots. up to infinite terms is

Options

  1. Alog⁡e9\log _e 9
  2. B00
  3. C11
  4. Dlog⁡e3\log _e 3

Correct answer

A. log⁡e9\log _e 9

Step-by-step solution

\frac{1}{\log _3 \mathrm{e}}+\frac{1}{\log _3 \mathrm{e}^2}+\frac{1}{\log _3 \mathrm{e}^4}+\ldots=\frac{1}{\log _3 \mathrm{e}}+\frac{1}{2 \log _3 \mathrm{e}}+\frac{1}{4 \log _3 \mathrm{e}}+\ldots \cdot\left(\right.Since,log⁡a\mathrmbm=mlogab)=log⁡e3+log⁡e32+log⁡e34+….(Since, \left.\log _{\mathrm{a}} \mathrmb^{\mathrm{m}}=\mathrm{m} \mathrm{log}_{\mathrm{a}} \mathrm{b}\right)=\log _{\mathrm{e}} 3+\frac{\log _{\mathrm{e}} 3}{2}+\frac{\log _{\mathrm{e}} 3}{4}+\ldots . \quad\left(\right. Since, \left.\log _{\mathrm{a}} \mathrm{b}=\frac{1}{\log _{\mathrm{b}} \mathrm{a}}\right)=\log _{\mathrm{e}} 3\left(1+\frac{1}{2}+\frac{1}{4}+\ldots.\right)=\log _{\mathrm{e}} 3\left(\frac{1}{1-\frac{1}{2}}\right)\left(\because 1, \frac{1}{2}, \frac{1}{4} \ldots\right.isG.P.witha=1,r=12)=log⁡e3(2)=2log⁡e3=log⁡e32=log⁡e9is G.P. with \left.\mathrm{a}=1, \mathrm{r}=\frac{1}{2}\right)=\log _{\mathrm{e}} 3(2)=2 \log _{\mathrm{e}} 3=\log _{\mathrm{e}} 3^2=\log _{\mathrm{e}} 9.
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