What is the explicit rule for the geometric sequence? 400, 200, 100, 50,...

(I'll put the answers in a screenshot) Plzz help :(

an = 400*(1/2)^(n - 1) which is C is the most common answer.

Step-by-step explanation:

What did you have to do to get 400 as the first term?

There are two answers.

an = 400 * (1/2)^(n - 1)

an = 400 * (1/2)^n

Which one is the answer?

The answer is the one that leaves 400 as the first term.

a1 = 400*(1/2)^(n-1) should be the answer.

400*(1/2)^n  is unfortunately sometimes used. In which case, the first term is a^0

A1 = 400 (1/2)^(n - 1) is the usual for that describes the series.