General forms of a Sequence

 Arithmetic & Geometric Sequences

Arithmetic formula: an= a1 (n + 1) d

Geometric formula: an= a1* r (n-1)

Example: -9, 3, -1, 1/3, 1/9    

This is a geometric sequence.

To find the term in a geometric sequence multiply or divide the previous term by “r”.

-9, 3, -1, 1/3, 1/9    r= -1/3  

5,   -10,   20,   -40    r= -2 

-10    20     -40

5      -10     20