00:01
Suppose we have a sequence that starts with negative 1, then positive 2, then negative 4, and so on.
00:07
Let's determine what the 10th term is going to be.
00:10
Well, we have a formula from the book stating that if we just know the first term, that is a1, and the common ratio r, we can determine the nth term for any n.
00:22
So we already know the first term, that's negative 1.
00:25
Let's determine the common ratio.
00:27
This is just any term divided by the previous, that is, negative 4 over 2, or 2 over negative 1.
00:34
In both cases, the answer to this is negative 2.
00:39
So that's our common ratio...