Question

6, 1, -4, -9,...

Answer 1

Texaschic nailed it when saying that it's arithmetic

The recursive way to write this is to say

$a_1 = 6$
$a_n = a_{n-1} - 5$

which tells us "start at 6 and each time subtract off 5"

The $a_n$ portion is the nth term while $a_{n-1}$ is the term just before the nth term