How can an expression or process be determined for an arithmetic sequence?

An aritmetic sequcne is represented as



where
an=nth term
a1=first term
d=common differnce, or how much each term increases by
n=which term

example

1,3,5, etc
first term is 1
common difference is 2 because it increases by 2 each time
so the formula would be


if we had
5,3,1
first term s 5
common difference is -2 since it goes up by -2 each time
so formula is


hope this helps

The answer is b: step 2.