Find the indicated partial sum for the given sequence with the given first term and general term.
-$\mathrm { s } _ { 4 } , \mathrm { a } _ { 1 } = 4 , \mathrm { a } _ { \mathrm { n } } = 20 \mathrm { a } _ { \mathrm { n } - 1 }$
A) $- 7582$
B) $- 7581$
C) 8419
D) 673,684

Question

Quizplus · Accepted Answer

The sequence is geometric with the first term $a_1 = 4$ and common ratio $r = 20$. The formula for the nth partial sum of a geometric sequence is $S_n = a_1 \frac{1-r^n}{1-r}$. Substituting $n = 4$, $a_1 = 4$, and $r = 20$, we get $S_4 = 4 \frac{1-20^4}{1-20}$, which simplifies to a positive value, specifically 673,684.

Find the Indicated Partial Sum for the Given Sequence with the Given