precalculus 12 grade

Question

What is a formula for the nth term of the given sequence?

10,50,250

1)an=10(1/5)^n

2) an=10(1/5)1-n

3)an=2(1/5)^1-n

Answer 1

If there is a typo in answer choice (2) and it should have been:

a_n = 10(1/5)^1-n

then that is the correct answer.

(1/5)^1-n = (1/5)^--(n-1) = 5^(n-1)

so

a_n = 10(5)^(n-1)

yields the series 10, 50, 250, ...

Answer 2

Common ratio is 5.

None of the choices are correct.