~ = sub
-arithmetic sequence
recursive=ex. a~2=a~1+3 equation is a~n=a~n-1+x
explicit= equation is a~n=4+3(n-1)
-geometric sequence
explicit= equation y=ab^x-1

d=difference
arithmetic: A~n=a~1+d(n-1)
geometric: a~n=a~1(r)^n-1