In this section we briefly state two results concerning series a_{n}
with terms a_{n} that are not necessarily ≥ 0. The first result has to do with
absolute convergence and the second with alternating series.

A series a_{n} is said to converge absolutely if
| a_{n}| converges. It is a theorem that if any series converges
absolutely, then it also converges.

A series a_{n} is said to be alternating if the a_{n} alternate
between being positive and negative. If a_{n} is an alternating series
such that | a_{n+1}|≤| a_{n}| for all n≥1 and a_{n} = 0,
then a_{n} converges. This is called the alternating series test.