Answer:
-3
Step-by-step explanation:
There are two ways to see what the next sequence number would be in this case.
First approach, you start with the first number (1) than count every other number, which are all positive integers. You do the same starting from the second number (-1), which would then be all negative integers.
Second approach, consider 2 consecutive numbers being a single element of the series... each has a number (1,2,3) with its positive and negative values.
