Find the sum of the first 8 terms of the geometric sequence if the first term is 9 and the common ratio is -3.

1 answer:

ivann1987 [24]3 years ago

5 0

hmmmm let's see $\bf \textit{sum of a finite geometric sequence}=S_n=a_1\left( \cfrac{1-r^n}{1-r} \right)
\\\\

\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term}\\
r=\textit{common ratio}
\end{cases}\qquad thus\implies S_8=9\left( \cfrac{1-(-3)^8}{1-(-3)} \right)$

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