Answer:
[tex]a_n= - 1( - 2)^{n-1}[/tex]
Step-by-step explanation:
The given geometric sequence is :
-1,2,-4,8,...
The first term is
[tex]a_1=-1[/tex]
The common ratio is
[tex]r = \frac{2}{ - 1} = - 2[/tex]
The nth term is given by;
[tex]a_n=a_1(r^{n-1})[/tex]
We substitute the values of the first term and common ratio to get:
[tex]a_n= - 1( - 2)^{n-1}[/tex]
This is called the explicit formula.
