Question

Find S11 for the geometric series 1 + 3 + 9 + 27 +…
A. 84,934
B. 88,573
C. 93,198
D. 96,143

Answer 1

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

n = sum of n terms = 11
a1 = first term = 1
r = common ratio = 3
now we sub
s11 = 1(1 - 3^11) / (1 - 3)
s11 = 1 (1 - 177147) / -2
s11 = 1 (-177146) / -2
s11 = -177146/-2
s11 = 88573