Question

Find the common ratio and the explicit formula

-3, 9, -27, 81,​

Answer 1

see explanation

Explanation:

These are the terms of a geometric sequence with n th term

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

where re a is the first term and r the common ratio

r = 9 ÷ - 3 = - 27 ÷ 9 = 81 ÷ - 27 = - 3 ← common ratio

and a = - 3, thus

[te x]a_{n}[/tex] = - 3
`(-3)^(n-1)` ← explicit formula