Question

what is the sum of a 7 term geometric sequence if the first term is -6 the last term is -24,567 and the common ratio is -4?

Answer 1

Sum = -19662

Explanation:

first term is -6

the last term is -24,567

and the common ratio is -4

Sum of geometric series formula is

`S_n = (a_1(1-r^n))/(1-r)`

a1 is the first term = -6

r is the common ratio = -4

n is the number of terms = 7

Plug in all the values in the formula

`S_n = (-6(1-(-4)^7))/(1-(-4))`

`S_7 = (-6(1 + 16384))/(5)= -19662`

Sum = -19662