Question

how do I find a1 for the given geometric series? sn= 688 r=1/2 an= 16

Answer 1

a1 = (1-r^n)/(1-r)

Answer 2

but I don't know what is n

Answer 3

I checked the answer and a1 is 1024, but I don't understand how did that happen?

Answer 4

I don't know what you mean by s(n) and a(n)

Answer 5

sn=688 the sum from a1 to an and an is the last number of the series
an is 16