Question

What is the 20th term of the arithmetic sequence 2, –4, –10, … ?

Answer 1

After the first term you obviously subtract `6` at every step.

Explanation:

At the 20th term you must have done this 19 times.
So the 20th term is `2-(19*6)=-112`

Watch it!
Most of the times the first term is called `t_0`.
This means that the 20th term is then `t_19`

But if they ask you for `t_20` (=21th) it's different:
`t_20=2-(20*6)=-118`