We take the function as a sequence
Term 1 ⇒ 5
Term 2 ⇒ 4
Term 3 ⇒ 3.2
Between terms, there is a common ratio of ⁴/₅
We get it from here:
Term 2 / Term 1 =
Term 3 / Term 2 =
=
When a sequence has a common ratio between term, the sequence is a Geometric Sequence
Where
is the first term, 
is the common ratio, and 
is the term number
We have:
and 
The formula for the function is
Term 1 ⇒ 5
Term 2 ⇒ 4
Term 3 ⇒ 3.2
Between terms, there is a common ratio of ⁴/₅
We get it from here:
Term 2 / Term 1 =
Term 3 / Term 2 =
When a sequence has a common ratio between term, the sequence is a Geometric Sequence
Where
We have:
The formula for the function is