# Math Help - Grade 11 help: Sequences

1. ## Grade 11 help: Sequences

When a sequence is NOT arithmetic OR geometric, how can you determine the formula for the nth term?

I do not understand how to get the formula when this situation occurs.

2. This depends on the series you're given. There's no formula or standard way of getting the $n-th$term in general. In the case of an arithmetic or geometric series it just so happens that the deriving a formula is easy and obvious. Do you have a specific series in mind?

3. Originally Posted by skeske1234
When a sequence is NOT arithmetic OR geometric, how can you determine the formula for the nth term?

I do not understand how to get the formula when this situation occurs.
$-1,\frac{1}{2},\frac{-1}{6},\frac{1}{24},\cdots$ can easily be identified to be $a_n=\frac{(-1)^n}{n!}$