Question

1.2, 3, 7.5, 18.75, ...

Which formula can be used to describe the sequence?

f(x) = 1.2(2.5)x – 1
f(x) = 2.5(1.2)x – 1
f(x) = 1.2(2.5)x
f(x) = 2.5(1.2)

Answer 1

Each term is multiplied by 2.5 to get the next, so it's geometric with first term 1.2 and ratio 2.5. The nth term is

a_n = 1.2(2.5)^(n−1).

So the correct choice (with x as the term index starting at 1) is: f(x) = 1.2(2.5)^(x−1).