Asked by anonymous

find Sn for geometric sequence with A1 = 8, n = 9, and r = -1

Sn = A1 = 8, n = 9 and r = -1

Sn = A1(1-r^n) / 1-r
= 8(1 - 1^-1)/(1-(-1))
= 8(0)/2
= 0

is this right ?
Answered by Mgraph
No.
Sn=8(1-(-1)^9)/(1-(-1))=8*2/2=8