Geometric Sequence = A sequence of numbers that you multiply by a number to get the next term.
e.g if you have the sequence 5,10,20,40,80
call the sequence 'a'
a1 = 5
a2 = 10 a2 = a1 x 2
a3 = 20 a3 = a2 x 2
a4 = 40 a4 = a3 x 2
a5 = 80 a5 = a4 x 2
if the sequence continued, we would get a100 = a99 x 2
in general, we would have ak+1 = ak x 2
this is called an iterative or inductive formula.