Question

Write the explicit formula for the geometric sequence.

a1 = -5 a2 = 20 a3 = -80

A. an = -5 • (-4)n

B. an = -5(-4)n-1

C. an = -4(-5)n-1

D. an = -5 • (4)n

Answer 1

What is the starting term and the common ratio?

Answer 2

Once you get those things, plug into:
An = A1 * (r)^(n-1)
where A1 is the starting term and r is the common ratio.

Answer 3

you can get the common ratio by dividing a term by the one before it