Question

What is the sum of the geometric sequence -3, 18, -108, if there are 7 terms?

a.411,772

b.-308,829

c.159,964

d.-119,973

Answer 1

common factor is r= -6
sum to n factors of GP is given by a{(r^n)-1}/r-1
so ur solution is (-3)[{(-6)^7}-1]/(-6-1)
(-3)[-279936-1]/(-7)
119973
making it option D

Answer 2

d. is negative but your answer is positive was that a typo? thank you so much for your help and thank you for actually typing out the problem @heybhai