Answer:
[tex]a_{n}[/tex] = 4 [tex](-5)^{n-1}[/tex]
Step-by-step explanation:
There is a common ratio r between consecutive terms , that is
r = - 20 ÷ 4 = 100 ÷ - 20 = - 5
This indicates the sequence is geometric with nth term ( explicit formula )
[tex]a_{n}[/tex] = a₁ [tex](r)^{n-1}[/tex]
where a₁ is the first term and r the common ratio
Here a₁ = 4 and r = - 5 , then
[tex]a_{n}[/tex] = 4 [tex](-5)^{n-1}[/tex]
