Select all the true statements about the sequence 8 16 32 64

Select all the true statements about the sequence.

8, -16, 32, -64, ...

a.) s₈ = -680

b.) the sequence is geometric

c.) The rule is a_n = 8(-2)^n-1

d.) a₈ = 2,048

8, -16, 32, -64, ......

sequence will be geometric if

a2/a1 = a3/a2 = a4/a3

-16/8 = 32/(-16) = (-64)/32 = -2

Since the ratio is constant, sequence is geometric.

rule will be = a1*r^(n - 1)

a1 = 9, r = -2

rule = 8*(-2)^(n - 1)

a8 = 8*(-2)^(8 - 1) = -1024

Sum of geometric series is given by:

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

S8 = 8*(1 - (-2)^8)/(1 - (-2)) = -680

Correct options are: A, B, C