What is a8 for the geometric sequence 6,561; −2,187; 729; −243; …6,561; −2,187; 729; −243; ….

Consider a geometric sequence 

let  and the common ratio be r, then the sequence is constructed as follows:



we can observe that each term of the sequence is its previous term * r.

In the given sequence, to find the common ratio we divide 6,561 by −2,187 and get -3. This means that 

Let the first term , 

then the eighth term is  



-3

1.17+3.99a. you combine the terms with a to create 3.99 and the 1.17 stays because it has no like terms or a variable