9 Partial sums of geometric series 9Ju
Find the fourth partial sum of the series.
\[
5+25+125+625+3125+15625+\cdots
\]
Write your answer as an integer or a fraction in simplest form
\[
S_{4}=
\]

Answer

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Answer

\(S_{4} = \frac{a_1(r^n - 1)}{r - 1} = \frac{5 (5^4 - 1)}{5 - 1}\)

Steps

Step 1 ：\(a_1 = 5\)

Step 2 ：\(r = 5\)

Step 3 ：\(S_{4} = \frac{a_1(r^n - 1)}{r - 1} = \frac{5 (5^4 - 1)}{5 - 1}\)