# Thread: Sequence A-Level Question

1. ## Sequence A-Level Question

Find the nth tern of the sequence
-3,5,-7,9

2. Originally Posted by helpishere
Find the nth tern of the sequence
-3,5,-7,9
$T_{n} = (-1)^n (2n + 1)$

First ignore the negatives.

It's easy to see that the n-th term is then given by $T_{n} = (2n + 1)$

Now we see that every odd term ( $T_1$ , $T_3$ , etc.) is negative.

So all we do is multiply the expression by $(-1)^n$ where $n$ is the term. So if it's and odd term, it will have a negative value and a positive value for an even term.