Which formula can be used to describe the sequence below?
27, 9, 3, 1, 1/

The nth term:  an = 27(1/3)^(n-1).

Also see below.

Step-by-step explanation:

Each term after the first is obtained by multiplying the previous term by 1/3.

It is a geometric sequence with first term 27 and common ratio 1/3.

The formula for the nth term an  is an = 27(1/3)^(n-1).

If you want the sigma notation formula for the sum of n terms of this series it is :

n

∑    27(1/3)^k         This gives the sum of the first n terms.

k=0

rotation point l

step-by-step explanation: