Terminology - Nth rule I'm trying to help my son study 8th grade math (in Texas).  He's having trouble with the "Nth rule".  Is anyone familiar with this terminology?  I think that it may be related to the Nth term in a series, but I also think that it has a more specific meaning.

What they mean is this: Suppose I give you a sequence like
2,4,6,8,...
Then I ask you: How can I obtain the n-th term in this sequence?
And you'll say: It's just $2n$.
Now, for sequences of the form $an + b$, it is quite easy to obtain the rule: Just look how the element increases in each step, this gives you $a$. Then see what the first element is and choose $b$ so that it's obtained for $n = 1$.
