Question

find s for the geometric series 4+12+36+108+.
20

Answer 1

first, you must use the geometric series formula for Sn
\[Sn= \frac{ a(r^n - 1) }{ (r-1) }\]

Answer 2

since S(20), that means n = 20
replace all the n in the formula to 20
and since the series is 3 times the previous number
4*3 =12
12*3=36
36*3=108
then r=3
and a=4
4 sequence

Answer 3

\[S_(20)=\frac{ 4(3^{20}-1 )}{ 3-1}\]