Question

For the following geometric sequence, find the explicit formula.

{1, -3, 9, ...}

an = (-3) n - 1
an = -3 · an - 1 where a1 = 1
an = -1 · (-3) n - 1
an = -3 · an - 1 where a1 = -1

Answer 1

Answer:
`a_n=(-3)^(n-1)`

Explanation:

The common ratio is
`r=-3`.

`a_n=a_1 \cdot r^(n-1)=1 \cdot (-3)^(n-1)=(-3)^(n-1)`