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Question: Answered & Verified by Expert
$1+\frac{3}{2}+\frac{5}{2^2}+\frac{7}{2^3}+\ldots \ldots \infty$ is equal to
MathematicsSequences and SeriesJEE Main
Options:
  • A $3$
  • B $6$
  • C $9$
  • D $12$
Solution:
1598 Upvotes Verified Answer
The correct answer is: $12$
It is an arithmetico-geometric series
$S_{\infty}=\frac{a}{1-r}+\frac{d r}{(1-r)^2}$ $=\frac{1}{1-\frac{1}{2}}+\frac{2}{\left(1-\frac{1}{2}\right)^2}=\frac{2}{\frac{1}{2}}+\frac{2}{\frac{1}{4}}$
$=4+8=12$.

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