# Algebra II

posted by
**anonymous**
.

find Sn for geometric sequence with a1 = 8, n = 9, and r = -1?

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

= 8(1-1)/(1+1) = 8(0)/2

= 0

is this correct..?

posted by
**anonymous**
.

find Sn for geometric sequence with a1 = 8, n = 9, and r = -1?

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

= 8(1-1)/(1+1) = 8(0)/2

= 0

is this correct..?