Question

What is the sum of the geometric sequence -4,24, -144, ... if there are 6 terms?

A. -159,963
B. 26,660
C. 26,661
D. 159,963

Answer 1

26,660

Explanation:

Answer 2

each term is multiplied by -6 to get next term
first term is -4

a1=-4
r=-6

the sum is

`S_n=(a_1(1-r^n))/(1-r)`
a1=-4
r=-6
n=6 because we want 6 terms


`S_6=(-4(1-(-6)^6))/(1-(-6))`

`S_6=(-4(1-46656))/(1+6)`

`S_6=(-4(-46655))/(7)`

`S_6=(186620)/(7)`

`S_6=26660`

answer is B