Find a formula for the general term of each sequence. Assume each sequence starts with n = 1.
-1, 3, -5, 7,...
If we ignore the signs we see the odd numbers (2n – 1). To have alternating signs with the first term negative, we multiply by (-1)n.
The general terms is
an = (-1)n(2n – 1).
Make sure you have proper parentheses in this expression, because
(-1)n2n – 1
means something different!