This is a geometric sequence because each term is a constant multiple, called the common ratio, of the previous term. In this case the common ratio, noted as "r", is:
8/-2=-32/8=128/-32=r=-4
The first term is -2
Any geometric sequence can be expressed as:
a(n)=ar^(n-1), a=initial term, r=common ratio, n=term number.
Since we know r and a for this problem already we can say:
a(n)=-2(-4)^(n-1)