Question

Find the sum of the first 13 terms of the geometric sequence shown below

4, 12, 36, 108, .........

The sum of the first 13 terms is?

Answer 1

4, 12 ,36, 108, 324, 972, 2916,8748, 26244, 78732, 236196, 708588, 2,125,764.
All the sums are multiplied by 3.

Answer 2

the sum of a geometric sequence with a common ratio or r and a fist term of a1 and summing to term n is

`(a_1(1-r^n))/(1-r)`
common ratio is 3=r
first term is 4
13 terms

`(4(1-3^13))/(1-3)`=

`(4(1-3^13))/(-2)`=
3188644