Answer:
[tex]a_n =-\frac{1}{4} \cdot a_{n-1}[/tex]
Step-by-step explanation:
{-80, 20, -5, ...}
General recusive formula for geometric sequence is
[tex]a_n = r \cdot a_{n-1}[/tex]
Where 'r' is the common ratio
To find common ratio 'r' we divide second term by first term
[tex]r=\frac{20}{-80} =-\frac{1}{4}[/tex]
Replace 'r' with -1/4
First term is -80
Recursive formula becomes
[tex]a_n =-\frac{1}{4} \cdot a_{n-1}[/tex]
