**Arithmetic**

General Term:

To figure out the value of any given term (), a (the first term), d (the common difference), or n (the term in which a certain value appears).

Sum of Terms:

To figure out the sum of any given arithmetic series (), n (the last term), or a (the first term).

**Geometric**

General Term:

To figure out any given term (), a (the first term), r (the common ratio), or n (the term in which a certain value appears).

Sum of Terms:

To figure out the partial sum of any geometric series if not given the last term, the last term, the first term, or the common ratio OR

to do the same thing, but if given the last term of the series.

You can have two types of geometric series: convergent (terms come closer together) or divergent (terms become further apart).

When you have a convergent series, the common ratio is greater than -1 but smaller than 1 (and cannot equal zero). Convergent series have infinite sums (the number in which the sum of all the terms converge at), which can be calculated with the formula .

Divergent series don’t have infinite sums.