Question

What is the value of a15 if a12= 1.7 and the recursive form of a geometric sequence is an= -3an-1?

Answer 1

\(a_{\color{red}{n}}=-3a_{\color {blue}{n-1}}\)
so, if n =15, then n-1=14, right?
You have
\(a_{\color{red}{15}}=-3a_{\color {blue}{14}}\)

and then go back one more step

\(a_{\color{red}{14}}=-3a_{\color {blue}{13}}\)

and then

\(a_{\color{red}{13}}=-3a_{\color {blue}{12}}\)

Answer 2

Now, you know that \(a_{12}=1.7\)
so, just calculate back to get \(a_{15}\)