<h2>Geometric progression</h2>

 A geometric progression, also known

 as a geometric sequence, 

is a sequence of non-zero numbers 

where each term after the first

 is found by multiplying the previous

 one by a fixed, non-zero number

 called the common ratio

 

For example the sequence

2,6,18,54

Is a geometric sequence (GP)

with common ratio r=3

 

The sequence  

36 , 18, 9, 9/2 

is a GP with common ratio  1/2

 

The general form of a geometric sequence is

${\displaystyle a,\ ar,\ ar^{2},\ ar^{3},\ ar^{4},\ \ldots }$

  a ≠ 0 and r ≠ 0