Question

Find the sum of an 8-term geometric sequence when the first term is 7 and the last term is 114,688 and select the correct answer below.

Answer 1

It is multiplied by 4 each time.

Answer 2

First term a1 = 7
8th term a1*r^7 = 114688

so r^7  =   114688/7 = 16384

r = 16384 ^ (1/7)  = 4

S8  = a1 * (r^n - 1 )/ (r - 1)   = 7 * (4^8 - 1) /  3  =   152,915  answer