what is an arithmetic sequence?

It's a sequence of numbers where there is a common difference, d, such that the difference between any two consecutive number is the same.

For example:

1, 4, 7, 10, 13 ...

2, 4, 6, 8, 10 ...

100, 90, 80, 70, 60 ...

How do the terms work?

The first term is n = 1 (called a1), the second term is n = 2 (called a2), etc.

For arithmetic series, there is a formula (of n) that can describe the series. If you plug in n=1, you get the first term. If you plug in n=2, you get the second term, etc.

Sometimes you might be able to figure this out by just thinking:

2, 4, 6, 8, 10 ...

Or, you can use this method:

Let's do some examples!