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Question: Answered & Verified by Expert
If $b$ is the first term of an infinite G. P whose sum is five, then $b$ lies in the interval.
MathematicsSequences and SeriesJEE MainJEE Main 2018 (15 Apr Shift 1 Online)
Options:
  • A
    $(-\infty,-10)$
  • B
    $(10, \infty)$
  • C
    $(0,10)$
  • D
    $(-10,0)$
Solution:
2050 Upvotes Verified Answer
The correct answer is:
$(0,10)$
First term $=b$ and common ratio $=\mathrm{r}$
For infinite series, Sum $=\frac{b}{1-r}=5$ $\Rightarrow b=5(1-\mathrm{r})$
So, interval of $b=(0,10)$ as, $-1 < \mathrm{r} < 1$ for infinite GP.

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