How do you find $S_{n}$ $S_n$ for the geometric series $a_{1} = 5$ $a_1=5$ , r=3, n=12?

Question

3491 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2018-01-22T17:27:21

$S_{n} = a_{1} \frac{r^{n} - 1}{r - 1}$ $S_n = a_1 (r^n-1)/(r-1)$

hence plugging in the values,

$S_{n} = 5 (\frac{3^{12} - 1}{3 - 1})$ $S_n = 5 ((3^12-1)/(3-1))$

$S_{n} = \frac{5}{2} (3^{12} - 1)$ $S_n = 5/2 (3^12-1)$

How do you find S_nSnS_n for the geometric series a_1=5a1=5a_1=5, r=3, n=12?