Question

5, 10, 20, 40, ...

Answer 1

5 10 20 40

10/5 = 2

20/10 = 2

40/20 = 2

Common ratio: $r=2$

Explicit formula: $a_n = 5 (2^{n-1})$

Recursive:

$a_{n+1} = 2 a_n$

$a_1 = 5$

This is a geometric sequence.