Sunday 27 January 2013

Help on Geometric Sequence Problem?

The sum of an infinite geometric series with first term
a and common ratio r < 1 is given by $ S_n=a\cdot\dfrac{r^n-1}{r-1} $.
The sum of a given infinite geometric series is $S_{\infty}=200 $ and the
common ratio $r$ is 0.15. What is the second term $a_2$ of this
series?



I'm confused on how to attack,can someone explain it to me? Thanks.

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