Question

What is the formula for the following geometric sequence?

-5, -10, -20, -40, ...

an = -5 · 2n - 1
an = -5 · (-2)n - 1
an = -2 · (-5)n - 1
an = 2 · (-5)n - 1

Answer 1

A

Explanation:

The n th term formula for a geometric sequence is

`a_(n)` = a
`(r)^(n-1)`

where a is the first term and r the common ratio

here a = - 5 and r = - 10 ÷ - 5 = 2, thus

`a_(n)` = - 5(
`2)^(n-1)` → A